Explore
Topics
Collections
Documents
FAQ
GitHub
Explore repos
Explore
Topics
Collections
Documents
FAQ
GitHub
Explore repos
Explore
/
C++
/
json
nlohmann
nlohmann/json
JSON for Modern C++
View on GitHub
Website / Demo
Copy link
Back to listing
50.8k
stars
7.5k
forks
100+
contributors
C++
README.md
View on GitHub
[](https://github.com/nlohmann/json/releases) [](https://ci.appveyor.com/project/nlohmann/json) [](https://github.com/nlohmann/json/actions?query=workflow%3AUbuntu) [](https://github.com/nlohmann/json/actions?query=workflow%3AmacOS) [](https://github.com/nlohmann/json/actions?query=workflow%3AWindows) [](https://coveralls.io/github/nlohmann/json?branch=develop) [](https://scan.coverity.com/projects/nlohmann-json) [](https://app.codacy.com/gh/nlohmann/json/dashboard?utm_source=gh&utm_medium=referral&utm_content=&utm_campaign=Badge_grade) [](https://issues.oss-fuzz.com/issues?q=project:json) [](https://wandbox.org/permlink/1mp10JbaANo6FUc7) [](https://json.nlohmann.me) [](https://raw.githubusercontent.com/nlohmann/json/develop/LICENSE.MIT) [](https://github.com/nlohmann/json/releases) [](https://github.com/nlohmann/json/releases) [](https://github.com/nlohmann/json/issues) [](https://isitmaintained.com/project/nlohmann/json "Average time to resolve an issue") [](https://www.bestpractices.dev/projects/289) [](https://scorecard.dev/viewer/?uri=github.com/nlohmann/json) [](https://cloudback.it) [](https://github.com/sponsors/nlohmann) [](https://api.reuse.software/info/github.com/nlohmann/json) [](https://discord.gg/6mrGXKvX7y) - [Design goals](#design-goals) - [Sponsors](#sponsors) - [Support](#support) ([documentation](https://json.nlohmann.me), [FAQ](https://json.nlohmann.me/home/faq/), [discussions](https://github.com/nlohmann/json/discussions), [API](https://json.nlohmann.me/api/basic_json/), [bug issues](https://github.com/nlohmann/json/issues)) - [Quick reference](#quick-reference) - [Examples](#examples) - [Read JSON from a file](#read-json-from-a-file) - [Creating `json` objects from JSON literals](#creating-json-objects-from-json-literals) - [JSON as a first-class data type](#json-as-a-first-class-data-type) - [Serialization / Deserialization](#serialization--deserialization) - [STL-like access](#stl-like-access) - [Conversion from STL containers](#conversion-from-stl-containers) - [JSON Pointer and JSON Patch](#json-pointer-and-json-patch) - [JSON Merge Patch](#json-merge-patch) - [Implicit conversions](#implicit-conversions) - [Conversions to/from arbitrary types](#arbitrary-types-conversions) - [Specializing enum conversion](#specializing-enum-conversion) - [Binary formats (BSON, CBOR, MessagePack, UBJSON, BJData, and BON8)](#binary-formats-bson-cbor-messagepack-ubjson-bjdata-and-bon8) - [Customers](#customers) - [Ecosystem](#ecosystem) - [Supported compilers](#supported-compilers) - [Integration](#integration) - [CMake](#cmake) - [Package Managers](#package-managers) - [Pkg-config](#pkg-config) - [License](#license) - [Contact](#contact) - [Security](#security) - [Thanks](#thanks) - [Used third-party tools](#used-third-party-tools) - [Notes](#notes) - [Execute unit tests](#execute-unit-tests) ## Design goals There are myriads of [JSON](https://json.org) libraries out there, and each may even have its reason to exist. Our class had these design goals: - **Intuitive syntax**. In languages such as Python, JSON feels like a first-class data type. We used all the operator magic of modern C++ to achieve the same feeling in your code. Check out the [examples below](#examples) and you'll know what I mean. - **Trivial integration**. Our whole code consists of a single header file [`json.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp). That's it. No library, no subproject, no dependencies, no complex build system. The class is written in vanilla C++11. All in all, everything should require no adjustment of your compiler flags or project settings. The library is also included in all popular [package managers](https://json.nlohmann.me/integration/package_managers/). - **Serious testing**. Our code is heavily [unit-tested](https://github.com/nlohmann/json/tree/develop/tests/src) and covers [100%](https://coveralls.io/r/nlohmann/json) of the code, including all exceptional behavior. Furthermore, we checked with [Valgrind](https://valgrind.org) and the [Clang Sanitizers](https://clang.llvm.org/docs/index.html) that there are no memory leaks. [Google OSS-Fuzz](https://github.com/google/oss-fuzz/tree/master/projects/json) additionally runs fuzz tests against all parsers 24/7, effectively executing billions of tests so far. To maintain high quality, the project is following the [OpenSSF Best Practices](https://www.bestpractices.dev/projects/289). See the [quality assurance](https://json.nlohmann.me/community/quality_assurance) overview documentation. Other aspects were not so important to us: - **Memory efficiency**. Each JSON object has an overhead of one pointer (the maximal size of a union) and one enumeration element (1 byte). The default generalization uses the following C++ data types: `std::string` for strings, `int64_t`, `uint64_t` or `double` for numbers, `std::map` for objects, `std::vector` for arrays, and `bool` for Booleans. However, you can template the generalized class `basic_json` to your needs. - **Speed**. There are certainly [faster JSON libraries](https://github.com/miloyip/nativejson-benchmark#parsing-time) out there. However, if your goal is to speed up your development by adding JSON support with a single header, then this library is the way to go. If you know how to use a `std::vector` or `std::map`, you are already set. See the [contribution guidelines](https://github.com/nlohmann/json/blob/develop/.github/CONTRIBUTING.md#please-dont) for more information. ## Sponsors You can sponsor this library at [GitHub Sponsors](https://github.com/sponsors/nlohmann). ### :raising_hand: Priority Sponsor - [Martti Laine](https://github.com/codeclown) - [Paul Harrington](https://github.com/phrrngtn) - [Mercedes-Benz Group](https://github.com/mercedes-benz) - [Ryan McCaffery](https://github.com/mccaffers) ### :label: Named Sponsors - [Michael Hartmann](https://github.com/reFX-Mike) - [Stefan Hagen](https://github.com/sthagen) - [Steve Sperandeo](https://github.com/homer6) - [Robert Jefe Lindstädt](https://github.com/eljefedelrodeodeljefe) - [Steve Wagner](https://github.com/ciroque) ### Further support The development of the library is further supported by JetBrains by providing free access to their IDE tools. [](https://jb.gg/OpenSourceSupport) Thanks everyone! ## Support :question: If you have a **question**, please check if it is already answered in the [**FAQ**](https://json.nlohmann.me/home/faq/) or the [**Q&A**](https://github.com/nlohmann/json/discussions/categories/q-a) section. If not, please [**ask a new question**](https://github.com/nlohmann/json/discussions/new) there. :books: If you want to **learn more** about how to use the library, check out the rest of the [**README**](#examples), have a look at [**code examples**](https://github.com/nlohmann/json/tree/develop/docs/mkdocs/docs/examples), or browse through the [**help pages**](https://json.nlohmann.me). :construction: If you want to understand the **API** better, check out the [**API Reference**](https://json.nlohmann.me/api/basic_json/) or have a look at the [quick reference](#quick-reference) below. :bug: If you found a **bug**, please check the [**FAQ**](https://json.nlohmann.me/home/faq/) if it is a known issue or the result of a design decision. Please also have a look at the [**issue list**](https://github.com/nlohmann/json/issues) before you [**create a new issue**](https://github.com/nlohmann/json/issues/new/choose). Please provide as much information as possible to help us understand and reproduce your issue. There is also a [**docset**](https://github.com/Kapeli/Dash-User-Contributions/tree/master/docsets/JSON_for_Modern_C%2B%2B) for the documentation browsers [Dash](https://kapeli.com/dash), [Velocity](https://velocity.silverlakesoftware.com), and [Zeal](https://zealdocs.org) that contains the full [documentation](https://json.nlohmann.me) as an offline resource. ## Quick reference - **Constructors**: [basic_json](https://json.nlohmann.me/api/basic_json/basic_json), [array](https://json.nlohmann.me/api/basic_json/array), [binary](https://json.nlohmann.me/api/basic_json/binary), [object](https://json.nlohmann.me/api/basic_json/object) - **Object inspection**: [type](https://json.nlohmann.me/api/basic_json/type), [operator value_t](https://json.nlohmann.me/api/basic_json/operator_value_t), [type_name](https://json.nlohmann.me/api/basic_json/type_name), [is_primitive](https://json.nlohmann.me/api/basic_json/is_primitive), [is_structured](https://json.nlohmann.me/api/basic_json/is_structured), [is_null](https://json.nlohmann.me/api/basic_json/is_null), [is_boolean](https://json.nlohmann.me/api/basic_json/is_boolean), [is_number](https://json.nlohmann.me/api/basic_json/is_number), [is_number_integer](https://json.nlohmann.me/api/basic_json/is_number_integer), [is_number_unsigned](https://json.nlohmann.me/api/basic_json/is_number_unsigned), [is_number_float](https://json.nlohmann.me/api/basic_json/is_number_float), [is_object](https://json.nlohmann.me/api/basic_json/is_object), [is_array](https://json.nlohmann.me/api/basic_json/is_array), [is_string](https://json.nlohmann.me/api/basic_json/is_string), [is_binary](https://json.nlohmann.me/api/basic_json/is_binary), [is_discarded](https://json.nlohmann.me/api/basic_json/is_discarded) - **Value access**: [get](https://json.nlohmann.me/api/basic_json/get), [get_to](https://json.nlohmann.me/api/basic_json/get_to), [get_ptr](https://json.nlohmann.me/api/basic_json/get_ptr), [get_ref](https://json.nlohmann.me/api/basic_json/get_ref), [operator ValueType](https://json.nlohmann.me/api/basic_json/operator_ValueType), [get_binary](https://json.nlohmann.me/api/basic_json/get_binary) - **Element access**: [at](https://json.nlohmann.me/api/basic_json/at), [operator[]](https://json.nlohmann.me/api/basic_json/operator[]), [value](https://json.nlohmann.me/api/basic_json/value), [front](https://json.nlohmann.me/api/basic_json/front), [back](https://json.nlohmann.me/api/basic_json/back) - **Lookup**: [find](https://json.nlohmann.me/api/basic_json/find), [count](https://json.nlohmann.me/api/basic_json/count), [contains](https://json.nlohmann.me/api/basic_json/contains) - **Iterators**: [begin](https://json.nlohmann.me/api/basic_json/begin), [cbegin](https://json.nlohmann.me/api/basic_json/cbegin), [end](https://json.nlohmann.me/api/basic_json/end), [cend](https://json.nlohmann.me/api/basic_json/cend), [rbegin](https://json.nlohmann.me/api/basic_json/rbegin), [rend](https://json.nlohmann.me/api/basic_json/rend), [crbegin](https://json.nlohmann.me/api/basic_json/crbegin), [crend](https://json.nlohmann.me/api/basic_json/crend), [items](https://json.nlohmann.me/api/basic_json/items) - **Capacity**: [empty](https://json.nlohmann.me/api/basic_json/empty), [size](https://json.nlohmann.me/api/basic_json/size), [max_size](https://json.nlohmann.me/api/basic_json/max_size) - **Modifiers**: [clear](https://json.nlohmann.me/api/basic_json/clear), [push_back](https://json.nlohmann.me/api/basic_json/push_back), [operator+=](https://json.nlohmann.me/api/basic_json/operator+=), [emplace_back](https://json.nlohmann.me/api/basic_json/emplace_back), [emplace](https://json.nlohmann.me/api/basic_json/emplace), [erase](https://json.nlohmann.me/api/basic_json/erase), [insert](https://json.nlohmann.me/api/basic_json/insert), [update](https://json.nlohmann.me/api/basic_json/update), [swap](https://json.nlohmann.me/api/basic_json/swap) - **Lexicographical comparison operators**: [operator==](https://json.nlohmann.me/api/basic_json/operator_eq), [operator!=](https://json.nlohmann.me/api/basic_json/operator_ne), [operator<](https://json.nlohmann.me/api/basic_json/operator_lt), [operator>](https://json.nlohmann.me/api/basic_json/operator_gt), [operator<=](https://json.nlohmann.me/api/basic_json/operator_le), [operator>=](https://json.nlohmann.me/api/basic_json/operator_ge), [operator<=>](https://json.nlohmann.me/api/basic_json/operator_spaceship) - **Serialization / Dumping**: [dump](https://json.nlohmann.me/api/basic_json/dump) - **Deserialization / Parsing**: [parse](https://json.nlohmann.me/api/basic_json/parse), [accept](https://json.nlohmann.me/api/basic_json/accept), [sax_parse](https://json.nlohmann.me/api/basic_json/sax_parse) - **JSON Pointer functions**: [flatten](https://json.nlohmann.me/api/basic_json/flatten), [unflatten](https://json.nlohmann.me/api/basic_json/unflatten) - **JSON Patch functions**: [patch](https://json.nlohmann.me/api/basic_json/patch), [patch_inplace](https://json.nlohmann.me/api/basic_json/patch_inplace), [diff](https://json.nlohmann.me/api/basic_json/diff), [merge_patch](https://json.nlohmann.me/api/basic_json/merge_patch) - **Static functions**: [meta](https://json.nlohmann.me/api/basic_json/meta), [get_allocator](https://json.nlohmann.me/api/basic_json/get_allocator) - **Binary formats**: [from_bjdata](https://json.nlohmann.me/api/basic_json/from_bjdata), [from_bon8](https://json.nlohmann.me/api/basic_json/from_bon8), [from_bson](https://json.nlohmann.me/api/basic_json/from_bson), [from_cbor](https://json.nlohmann.me/api/basic_json/from_cbor), [from_msgpack](https://json.nlohmann.me/api/basic_json/from_msgpack), [from_ubjson](https://json.nlohmann.me/api/basic_json/from_ubjson), [to_bjdata](https://json.nlohmann.me/api/basic_json/to_bjdata), [to_bon8](https://json.nlohmann.me/api/basic_json/to_bon8), [to_bson](https://json.nlohmann.me/api/basic_json/to_bson), [to_cbor](https://json.nlohmann.me/api/basic_json/to_cbor), [to_msgpack](https://json.nlohmann.me/api/basic_json/to_msgpack), [to_ubjson](https://json.nlohmann.me/api/basic_json/to_ubjson) - **Non-member functions**: [operator<<](https://json.nlohmann.me/api/operator_ltlt/), [operator>>](https://json.nlohmann.me/api/operator_gtgt/), [to_string](https://json.nlohmann.me/api/basic_json/to_string) - **Literals**: [operator""_json](https://json.nlohmann.me/api/operator_literal_json) - **Helper classes**: [std::hash<basic_json>](https://json.nlohmann.me/api/basic_json/std_hash), [std::swap<basic_json>](https://json.nlohmann.me/api/basic_json/std_swap) [**Full API documentation**](https://json.nlohmann.me/api/basic_json/) ## Examples Here are some examples to give you an idea how to use the class. Besides the examples below, you may want to: → Check the [documentation](https://json.nlohmann.me/)\ → Browse the [standalone example files](https://github.com/nlohmann/json/tree/develop/docs/mkdocs/docs/examples)\ → Read the full [API Documentation](https://json.nlohmann.me/api/basic_json/) with self-contained examples for every function ### Read JSON from a file The `json` class provides an API for manipulating a JSON value. To create a `json` object by reading a JSON file: ```cpp #include <fstream> #include <nlohmann/json.hpp> using json = nlohmann::json; // ... std::ifstream f("example.json"); json data = json::parse(f); ``` If using modules (enabled with `NLOHMANN_JSON_BUILD_MODULES`), this example becomes: ```cpp import std; import nlohmann.json; using json = nlohmann::json; // ... std::ifstream f("example.json"); json data = json::parse(f); ``` ### Creating `json` objects from JSON literals Assume you want to hard-code this literal JSON value as a `json` object: ```json { "pi": 3.141, "happy": true } ``` There are various options: ```cpp // Using (raw) string literals and json::parse json ex1 = json::parse(R"( { "pi": 3.141, "happy": true } )"); // Using user-defined (raw) string literals using namespace nlohmann::literals; json ex2 = R"( { "pi": 3.141, "happy": true } )"_json; // Using initializer lists json ex3 = { {"happy", true}, {"pi", 3.141}, }; ``` ### JSON as a first-class data type Here are some examples to give you an idea how to use the class. Assume you want to create the JSON object ```json { "pi": 3.141, "happy": true, "name": "Niels", "nothing": null, "answer": { "everything": 42 }, "list": [1, 0, 2], "object": { "currency": "USD", "value": 42.99 } } ``` With this library, you could write: ```cpp // create an empty structure (null) json j; // add a number stored as double (note the implicit conversion of j to an object) j["pi"] = 3.141; // add a Boolean stored as bool j["happy"] = true; // add a string stored as std::string j["name"] = "Niels"; // add another null object by passing nullptr j["nothing"] = nullptr; // add an object inside the object j["answer"]["everything"] = 42; // add an array stored as std::vector (using an initializer list) j["list"] = { 1, 0, 2 }; // add another object (using an initializer list of pairs) j["object"] = { {"currency", "USD"}, {"value", 42.99} }; // instead, you could also write (which looks very similar to the JSON above) json j2 = { {"pi", 3.141}, {"happy", true}, {"name", "Niels"}, {"nothing", nullptr}, {"answer", { {"everything", 42} }}, {"list", {1, 0, 2}}, {"object", { {"currency", "USD"}, {"value", 42.99} }} }; ``` Note that in all these cases, you never need to "tell" the compiler which JSON value type you want to use. If you want to be explicit or express some edge cases, the functions [`json::array()`](https://json.nlohmann.me/api/basic_json/array/) and [`json::object()`](https://json.nlohmann.me/api/basic_json/object/) will help: ```cpp // a way to express the empty array [] json empty_array_explicit = json::array(); // ways to express the empty object {} json empty_object_implicit = json({}); json empty_object_explicit = json::object(); // a way to express an _array_ of key/value pairs [["currency", "USD"], ["value", 42.99]] json array_not_object = json::array({ {"currency", "USD"}, {"value", 42.99} }); ``` ### Serialization / Deserialization #### To/from strings You can create a JSON value (deserialization) by appending `_json` to a string literal: ```cpp // create object from string literal json j = "{ \"happy\": true, \"pi\": 3.141 }"_json; // or even nicer with a raw string literal auto j2 = R"( { "happy": true, "pi": 3.141 } )"_json; ``` Note that without appending the `_json` suffix, the passed string literal is not parsed, but just used as JSON string value. That is, `json j = "{ \"happy\": true, \"pi\": 3.141 }"` would just store the string `"{ "happy": true, "pi": 3.141 }"` rather than parsing the actual object. The string literal should be brought into scope with `using namespace nlohmann::literals;` (see [`json::parse()`](https://json.nlohmann.me/api/operator_literal_json/)). The above example can also be expressed explicitly using [`json::parse()`](https://json.nlohmann.me/api/basic_json/parse/): ```cpp // parse explicitly auto j3 = json::parse(R"({"happy": true, "pi": 3.141})"); ``` You can also get a string representation of a JSON value (serialize): ```cpp // explicit conversion to string std::string s = j.dump(); // {"happy":true,"pi":3.141} // serialization with pretty printing // pass in the amount of spaces to indent std::cout << j.dump(4) << std::endl; // { // "happy": true, // "pi": 3.141 // } ``` Note the difference between serialization and assignment: ```cpp // store a string in a JSON value json j_string = "this is a string"; // retrieve the string value auto cpp_string = j_string.get<std::string>(); // retrieve the string value (alternative when a variable already exists) std::string cpp_string2; j_string.get_to(cpp_string2); // retrieve the serialized value (explicit JSON serialization) std::string serialized_string = j_string.dump(); // output of original string std::cout << cpp_string << " == " << cpp_string2 << " == " << j_string.get<std::string>() << '\n'; // output of serialized value std::cout << j_string << " == " << serialized_string << std::endl; ``` [`.dump()`](https://json.nlohmann.me/api/basic_json/dump/) returns the originally stored string value. Note the library only supports UTF-8. When you store strings with different encodings in the library, calling [`dump()`](https://json.nlohmann.me/api/basic_json/dump/) may throw an exception unless `json::error_handler_t::replace`, `json::error_handler_t::ignore`, or `json::error_handler_t::keep` are used as error handlers. #### To/from streams (e.g., files, string streams) You can also use streams to serialize and deserialize: ```cpp // deserialize from standard input json j; std::cin >> j; // serialize to standard output std::cout << j; // the setw manipulator was overloaded to set the indentation for pretty printing std::cout << std::setw(4) << j << std::endl; ``` These operators work for any subclasses of `std::istream` or `std::ostream`. Here is the same example with files: ```cpp // read a JSON file std::ifstream i("file.json"); json j; i >> j; // write prettified JSON to another file std::ofstream o("pretty.json"); o << std::setw(4) << j << std::endl; ``` Please note that setting the exception bit for `failbit` is inappropriate for this use case. It will result in program termination due to the `noexcept` specifier in use. #### Read from iterator range You can also parse JSON from an iterator range; that is, from any container accessible by iterators whose `value_type` is an integral type of 1, 2, or 4 bytes, which will be interpreted as UTF-8, UTF-16, and UTF-32 respectively. For instance, a `std::vector<std::uint8_t>`, or a `std::list<std::uint16_t>`: ```cpp std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'}; json j = json::parse(v.begin(), v.end()); ``` You may leave the iterators for the range [begin, end): ```cpp std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'}; json j = json::parse(v); ``` #### Custom data source Since the parse function accepts arbitrary iterator ranges, you can provide your own data sources by implementing the `LegacyInputIterator` concept. ```cpp struct MyContainer { void advance(); const char& get_current(); }; struct MyIterator { using difference_type = std::ptrdiff_t; using value_type = char; using pointer = const char*; using reference = const char&; using iterator_category = std::input_iterator_tag; explicit MyIterator(MyContainer* tgt = nullptr) : target(tgt) {} MyIterator& operator++() { target->advance(); return *this; } bool operator!=(const MyIterator& rhs) const { return rhs.target != target; } reference operator*() const { return target->get_current(); } MyContainer* target = nullptr; }; MyIterator begin(MyContainer& tgt) { return MyIterator{&tgt}; } MyIterator end(const MyContainer&) { return MyIterator{}; } void foo() { MyContainer c; json j = json::parse(begin(c), end(c)); } ``` #### SAX interface The library uses a SAX-like interface with the following functions: ```cpp // called when null is parsed bool null(); // called when a boolean is parsed; value is passed bool boolean(bool val); // called when a signed or unsigned integer number is parsed; value is passed bool number_integer(number_integer_t val); bool number_unsigned(number_unsigned_t val); // called when a floating-point number is parsed; value and original string is passed bool number_float(number_float_t val, const string_t& s); // called when a string is parsed; value is passed and can be safely moved away bool string(string_t& val); // called when a binary value is parsed; value is passed and can be safely moved away bool binary(binary_t& val); // called when an object or array begins or ends, resp. The number of elements is passed (or -1 if not known) bool start_object(std::size_t elements); bool end_object(); bool start_array(std::size_t elements); bool end_array(); // called when an object key is parsed; value is passed and can be safely moved away bool key(string_t& val); // called when a parse error occurs; byte position, the last token, and an exception is passed bool parse_error(std::size_t position, const std::string& last_token, const detail::exception& ex); ``` The return value of each function determines whether parsing should proceed. To implement your own SAX handler, proceed as follows: 1. Implement the SAX interface in a class. You can use class `nlohmann::json_sax<json>` as base class, but you can also use any class where the functions described above are implemented and public. 2. Create an object of your SAX interface class, e.g. `my_sax`. 3. Call `bool json::sax_parse(input, &my_sax)`; where the first parameter can be any input like a string or an input stream and the second parameter is a pointer to your SAX interface. Note the `sax_parse` function only returns a `bool` indicating the result of the last executed SAX event. It does not return a `json` value - it is up to you to decide what to do with the SAX events. Furthermore, no exceptions are thrown in case of a parse error -- it is up to you what to do with the exception object passed to your `parse_error` implementation. Internally, the SAX interface is used for the DOM parser (class `json_sax_dom_parser`) as well as the acceptor (`json_sax_acceptor`), see file [`json_sax.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/input/json_sax.hpp). ### STL-like access We designed the JSON class to behave just like an STL container. In fact, it satisfies the [**ReversibleContainer**](https://en.cppreference.com/w/cpp/named_req/ReversibleContainer) requirement. ```cpp // create an array using push_back json j; j.push_back("foo"); j.push_back(1); j.push_back(true); // also use emplace_back j.emplace_back(1.78); // iterate the array for (json::iterator it = j.begin(); it != j.end(); ++it) { std::cout << *it << '\n'; } // range-based for for (auto& element : j) { std::cout << element << '\n'; } // getter/setter const auto tmp = j[0].get<std::string>(); j[1] = 42; bool foo = j.at(2); // comparison j == R"(["foo", 1, true, 1.78])"_json; // true // other stuff j.size(); // 4 entries j.empty(); // false j.type(); // json::value_t::array j.clear(); // the array is empty again // convenience type checkers j.is_null(); j.is_boolean(); j.is_number(); j.is_object(); j.is_array(); j.is_string(); // create an object json o; o["foo"] = 23; o["bar"] = false; o["baz"] = 3.141; // also use emplace o.emplace("weather", "sunny"); // special iterator member functions for objects for (json::iterator it = o.begin(); it != o.end(); ++it) { std::cout << it.key() << " : " << it.value() << "\n"; } // the same code as range for for (auto& el : o.items()) { std::cout << el.key() << " : " << el.value() << "\n"; } // even easier with structured bindings (C++17) for (auto& [key, value] : o.items()) { std::cout << key << " : " << value << "\n"; } // find an entry if (o.contains("foo")) { // there is an entry with key "foo" } // or via find and an iterator if (o.find("foo") != o.end()) { // there is an entry with key "foo" } // or simpler using count() int foo_present = o.count("foo"); // 1 int fob_present = o.count("fob"); // 0 // delete an entry o.erase("foo"); ``` ### Conversion from STL containers Any sequence container (`std::array`, `std::vector`, `std::deque`, `std::forward_list`, `std::list`) whose values can be used to construct JSON values (e.g., integers, floating point numbers, Booleans, string types, or again STL containers described in this section) can be used to create a JSON array. The same holds for similar associative containers (`std::set`, `std::multiset`, `std::unordered_set`, `std::unordered_multiset`), but in these cases the order of the elements of the array depends on how the elements are ordered in the respective STL container. ```cpp std::vector<int> c_vector {1, 2, 3, 4}; json j_vec(c_vector); // [1, 2, 3, 4] std::deque<double> c_deque {1.2, 2.3, 3.4, 5.6}; json j_deque(c_deque); // [1.2, 2.3, 3.4, 5.6] std::list<bool> c_list {true, true, false, true}; json j_list(c_list); // [true, true, false, true] std::forward_list<int64_t> c_flist {12345678909876, 23456789098765, 34567890987654, 45678909876543}; json j_flist(c_flist); // [12345678909876, 23456789098765, 34567890987654, 45678909876543] std::array<unsigned long, 4> c_array {{1, 2, 3, 4}}; json j_array(c_array); // [1, 2, 3, 4] std::set<std::string> c_set {"one", "two", "three", "four", "one"}; json j_set(c_set); // only one entry for "one" is used // ["four", "one", "three", "two"] std::unordered_set<std::string> c_uset {"one", "two", "three", "four", "one"}; json j_uset(c_uset); // only one entry for "one" is used // maybe ["two", "three", "four", "one"] std::multiset<std::string> c_mset {"one", "two", "one", "four"}; json j_mset(c_mset); // both entries for "one" are used // maybe ["one", "two", "one", "four"] std::unordered_multiset<std::string> c_umset {"one", "two", "one", "four"}; json j_umset(c_umset); // both entries for "one" are used // maybe ["one", "two", "one", "four"] ``` Likewise, any associative key-value containers (`std::map`, `std::multimap`, `std::unordered_map`, `std::unordered_multimap`) whose keys can construct an `std::string` and whose values can be used to construct JSON values (see examples above) can be used to create a JSON object. Note that in case of multimaps, only one key is used in the JSON object and the value depends on the internal order of the STL container. ```cpp std::map<std::string, int> c_map { {"one", 1}, {"two", 2}, {"three", 3} }; json j_map(c_map); // {"one": 1, "three": 3, "two": 2 } std::unordered_map<const char*, double> c_umap { {"one", 1.2}, {"two", 2.3}, {"three", 3.4} }; json j_umap(c_umap); // {"one": 1.2, "two": 2.3, "three": 3.4} std::multimap<std::string, bool> c_mmap { {"one", true}, {"two", true}, {"three", false}, {"three", true} }; json j_mmap(c_mmap); // only one entry for key "three" is used // maybe {"one": true, "two": true, "three": true} std::unordered_multimap<std::string, bool> c_ummap { {"one", true}, {"two", true}, {"three", false}, {"three", true} }; json j_ummap(c_ummap); // only one entry for key "three" is used // maybe {"one": true, "two": true, "three": true} ``` ### JSON Pointer and JSON Patch The library supports **JSON Pointer** ([RFC 6901](https://tools.ietf.org/html/rfc6901)) as an alternative means to address structured values. On top of this, **JSON Patch** ([RFC 6902](https://tools.ietf.org/html/rfc6902)) allows describing differences between two JSON values -- effectively allowing patch and diff operations known from Unix. ```cpp // a JSON value json j_original = R"({ "baz": ["one", "two", "three"], "foo": "bar" })"_json; // access members with a JSON pointer (RFC 6901) j_original["/baz/1"_json_pointer]; // "two" // a JSON patch (RFC 6902) json j_patch = R"([ { "op": "replace", "path": "/baz", "value": "boo" }, { "op": "add", "path": "/hello", "value": ["world"] }, { "op": "remove", "path": "/foo"} ])"_json; // apply the patch json j_result = j_original.patch(j_patch); // { // "baz": "boo", // "hello": ["world"] // } // calculate a JSON patch from two JSON values json::diff(j_result, j_original); // [ // { "op":" replace", "path": "/baz", "value": ["one", "two", "three"] }, // { "op": "remove","path": "/hello" }, // { "op": "add", "path": "/foo", "value": "bar" } // ] ``` ### JSON Merge Patch The library supports **JSON Merge Patch** ([RFC 7386](https://tools.ietf.org/html/rfc7386)) as a patch format. Instead of using JSON Pointer (see above) to specify values to be manipulated, it describes the changes using a syntax that closely mimics the document being modified. ```cpp // a JSON value json j_document = R"({ "a": "b", "c": { "d": "e", "f": "g" } })"_json; // a patch json j_patch = R"({ "a":"z", "c": { "f": null } })"_json; // apply the patch j_document.merge_patch(j_patch); // { // "a": "z", // "c": { // "d": "e" // } // } ``` ### Implicit conversions Supported types can be implicitly converted to JSON values. It is recommended to **NOT USE** implicit conversions **FROM** a JSON value. You can find more details about this recommendation [here](https://www.github.com/nlohmann/json/issues/958). You can switch off implicit conversions by defining `JSON_USE_IMPLICIT_CONVERSIONS` to `0` before including the `json.hpp` header. When using CMake, you can also achieve this by setting the option `JSON_ImplicitConversions` to `OFF`. ```cpp // strings std::string s1 = "Hello, world!"; json js = s1; auto s2 = js.get<std::string>(); // NOT RECOMMENDED std::string s3 = js; std::string s4; s4 = js; // Booleans bool b1 = true; json jb = b1; auto b2 = jb.get<bool>(); // NOT RECOMMENDED bool b3 = jb; bool b4; b4 = jb; // numbers int i = 42; json jn = i; auto f = jn.get<double>(); // NOT RECOMMENDED double f2 = jn; double f3; f3 = jn; // etc. ``` Note that `char` types are not automatically converted to JSON strings, but to integer numbers. A conversion to a string must be specified explicitly: ```cpp char ch = 'A'; // ASCII value 65 json j_default = ch; // stores integer number 65 json j_string = std::string(1, ch); // stores string "A" ``` ### Arbitrary types conversions Every type can be serialized in JSON, not just STL containers and scalar types. Usually, you would do something along those lines: ```cpp namespace ns { // a simple struct to model a person struct person { std::string name; std::string address; int age; }; } ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60}; // convert to JSON: copy each value into the JSON object json j; j["name"] = p.name; j["address"] = p.address; j["age"] = p.age; // ... // convert from JSON: copy each value from the JSON object ns::person p { j["name"].get<std::string>(), j["address"].get<std::string>(), j["age"].get<int>() }; ``` It works, but that's quite a lot of boilerplate... Fortunately, there's a better way: ```cpp // create a person ns::person p {"Ned Flanders", "744 Evergreen Terrace", 60}; // conversion: person -> json json j = p; std::cout << j << std::endl; // {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"} // conversion: json -> person auto p2 = j.get<ns::person>(); // that's it assert(p == p2); ``` #### Basic usage To make this work with one of your types, you only need to provide two functions: ```cpp using json = nlohmann::json; namespace ns { void to_json(json& j, const person& p) { j = json{{"name", p.name}, {"address", p.address}, {"age", p.age}}; } void from_json(const json& j, person& p) { j.at("name").get_to(p.name); j.at("address").get_to(p.address); j.at("age").get_to(p.age); } } // namespace ns ``` That's all! When calling the `json` constructor with your type, your custom `to_json` method will be automatically called. Likewise, when calling `get<your_type>()` or `get_to(your_type&)`, the `from_json` method will be called. Some important things: - Those methods **MUST** be in your type's namespace (which can be the global namespace), or the library will not be able to locate them (in this example, they are in namespace `ns`, where `person` is defined). - Those methods **MUST** be available (e.g., proper headers must be included) everywhere you use these conversions. Look at [issue 1108](https://github.com/nlohmann/json/issues/1108) for errors that may occur otherwise. - When using `get<your_type>()`, `your_type` **MUST** be [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible). (There is a way to bypass this requirement described later.) - In function `from_json`, use function [`at()`](https://json.nlohmann.me/api/basic_json/at/) to access the object values rather than `operator[]`. In case a key does not exist, `at` throws an exception that you can handle, whereas `operator[]` exhibits undefined behavior. - You do not need to add serializers or deserializers for STL types like `std::vector`: the library already implements these. #### Simplify your life with macros If you just want to serialize/deserialize some structs, the `to_json`/`from_json` functions can be a lot of boilerplate. There are [**several macros**](https://json.nlohmann.me/api/macros/#serializationdeserialization-macros) to make your life easier as long as you want to use a JSON object as serialization. Which macro to choose depends on whether private member variables need to be accessed, a deserialization is needed, missing values should yield an error or should be replaced by default values, and if derived classes are used. See [this overview to choose the right one for your use case](https://json.nlohmann.me/features/arbitrary_types/#simplify-your-life-with-macros). ##### Example usage of macros The `to_json`/`from_json` functions for the `person` struct above can be created with [`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/). In all macros, the first parameter is the name of the class/struct, and all remaining parameters name the members. ```cpp namespace ns { NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person, name, address, age) } ``` If you want to inherit the `person` struct and add a field to it, it can be done with: ```cpp namespace ns { struct person_derived : person { std::string email; }; NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(person_derived, person, email) } ``` Here is another example with private members, where [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/) is needed: ```cpp namespace ns { class address { private: std::string street; int housenumber; int postcode; public: NLOHMANN_DEFINE_TYPE_INTRUSIVE(address, street, housenumber, postcode) }; } ``` Or in case if you use some naming convention that you do not want to expose to JSON: ```cpp namespace ns { class address { private: std::string m_street; int m_housenumber; int m_postcode; public: NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES(address, "street", m_street, "housenumber", m_housenumber, "postcode", m_postcode) }; } ``` #### How do I convert third-party types? This requires a bit more advanced technique. But first, let's see how this conversion mechanism works: The library uses **JSON Serializers** to convert types to JSON. The default serializer for `nlohmann::json` is `nlohmann::adl_serializer` (ADL means [Argument-Dependent Lookup](https://en.cppreference.com/w/cpp/language/adl)). It is implemented like this (simplified): ```cpp template <typename T> struct adl_serializer { static void to_json(json& j, const T& value) { // calls the "to_json" method in T's namespace } static void from_json(const json& j, T& value) { // same thing, but with the "from_json" method } }; ``` This serializer works fine when you have control over the type's namespace. However, what about `boost::optional` or `std::filesystem::path` (C++17)? Hijacking the `boost` namespace is pretty bad, and it's illegal to add something other than template specializations to `std`... To solve this, you need to add a specialization of `adl_serializer` to the `nlohmann` namespace, here's an example: ```cpp // partial specialization (full specialization works too) namespace nlohmann { template <typename T> struct adl_serializer<boost::optional<T>> { static void to_json(json& j, const boost::optional<T>& opt) { if (opt == boost::none) { j = nullptr; } else { j = *opt; // this will call adl_serializer<T>::to_json which will // find the free function to_json in T's namespace! } } static void from_json(const json& j, boost::optional<T>& opt) { if (j.is_null()) { opt = boost::none; } else { opt = j.get<T>(); // same as above, but with // adl_serializer<T>::from_json } } }; } ``` #### How can I use `get()` for non-default constructible/non-copyable types? There is a way if your type is [MoveConstructible](https://en.cppreference.com/w/cpp/named_req/MoveConstructible). You will need to specialize the `adl_serializer` as well, but with a special `from_json` overload: ```cpp struct move_only_type { move_only_type() = delete; move_only_type(int ii): i(ii) {} move_only_type(const move_only_type&) = delete; move_only_type(move_only_type&&) = default; int i; }; namespace nlohmann { template <> struct adl_serializer<move_only_type> { // note: the return type is no longer 'void', and the method only takes // one argument static move_only_type from_json(const json& j) { return {j.get<int>()}; } // Here's the catch! You must provide a to_json method! Otherwise, you // will not be able to convert move_only_type to json, since you fully // specialized adl_serializer on that type static void to_json(json& j, move_only_type t) { j = t.i; } }; } ``` #### Can I write my own serializer? (Advanced use) Yes. You might want to take a look at [`unit-udt.cpp`](https://github.com/nlohmann/json/blob/develop/tests/src/unit-udt.cpp) in the test suite, to see a few examples. If you write your own serializer, you'll need to do a few things: - use a different `basic_json` alias than `nlohmann::json` (the last template parameter of `basic_json` is the `JSONSerializer`) - use your `basic_json` alias (or a template parameter) in all your `to_json`/`from_json` methods - use `nlohmann::to_json` and `nlohmann::from_json` when you need ADL Here is an example, without simplifications, that only accepts types with a size <= 32, and uses ADL. ```cpp // You should use void as a second template argument // if you don't need compile-time checks on T template<typename T, typename SFINAE = typename std::enable_if<sizeof(T) <= 32>::type> struct less_than_32_serializer { template <typename BasicJsonType> static void to_json(BasicJsonType& j, T value) { // we want to use ADL, and call the correct to_json overload using nlohmann::to_json; // this method is called by adl_serializer, // this is where the magic happens to_json(j, value); } template <typename BasicJsonType> static void from_json(const BasicJsonType& j, T& value) { // same thing here using nlohmann::from_json; from_json(j, value); } }; ``` Be **very** careful when reimplementing your serializer, you can stack overflow if you don't pay attention: ```cpp template <typename T, void> struct bad_serializer { template <typename BasicJsonType> static void to_json(BasicJsonType& j, const T& value) { // this calls BasicJsonType::json_serializer<T>::to_json(j, value) // if BasicJsonType::json_serializer == bad_serializer ... oops! j = value; } template <typename BasicJsonType> static void to_json(const BasicJsonType& j, T& value) { // this calls BasicJsonType::json_serializer<T>::from_json(j, value) // if BasicJsonType::json_serializer == bad_serializer ... oops! value = j.get<T>(); // oops! } }; ``` ### Specializing enum conversion By default, enum values are serialized to JSON as integers. In some cases, this could result in undesired behavior. If an enum is modified or re-ordered after data has been serialized to JSON, the later deserialized JSON data may be undefined or a different enum value than was originally intended. It is possible to more precisely specify how a given enum is mapped to and from JSON as shown below: ```cpp // example enum type declaration enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED, TS_INVALID=-1, }; // map TaskState values to JSON as strings NLOHMANN_JSON_SERIALIZE_ENUM( TaskState, { {TS_INVALID, nullptr}, {TS_STOPPED, "stopped"}, {TS_RUNNING, "running"}, {TS_COMPLETED, "completed"}, }) ``` The `NLOHMANN_JSON_SERIALIZE_ENUM()` macro declares a set of `to_json()` / `from_json()` functions for type `TaskState` while avoiding repetition and boilerplate serialization code. **Usage:** ```cpp // enum to JSON as string json j = TS_STOPPED; assert(j == "stopped"); // json string to enum json j3 = "running"; assert(j3.get<TaskState>() == TS_RUNNING); // undefined json value to enum (where the first map entry above is the default) json jPi = 3.14; assert(jPi.get<TaskState>() == TS_INVALID); ``` Just as in [Arbitrary Type Conversions](#arbitrary-types-conversions) above, - `NLOHMANN_JSON_SERIALIZE_ENUM()` MUST be declared in your enum type's namespace (which can be the global namespace), or the library will not be able to locate it, and it will default to integer serialization. - It MUST be available (e.g., proper headers must be included) everywhere you use the conversions. Other Important points: - When using `get<ENUM_TYPE>()`, undefined JSON values will default to the first pair specified in your map. Select this default pair carefully. If you desire an exception in this circumstance use `NLOHMANN_JSON_SERIALIZE_ENUM_STRICT()` which behaves identically except for throwing an exception on unrecognized values. - If an enum or JSON value is specified more than once in your map, the first matching occurrence from the top of the map will be returned when converting to or from JSON. ### Binary formats (BSON, CBOR, MessagePack, UBJSON, BJData, and BON8) Though JSON is a ubiquitous data format, it is not a very compact format suitable for data exchange, for instance over a network. Hence, the library supports [BSON](https://bsonspec.org) (Binary JSON), [CBOR](https://cbor.io) (Concise Binary Object Representation), [MessagePack](https://msgpack.org), [UBJSON](https://ubjson.org) (Universal Binary JSON Specification), [BJData](https://neurojson.org/bjdata) (Binary JData), and [BON8](https://github.com/hikoworks/hikogui/blob/main/docs/BON8.md) (Binary Object Notation 8) to efficiently encode JSON values to byte vectors and to decode such vectors. ```cpp // create a JSON value json j = R"({"compact": true, "schema": 0})"_json; // serialize to BSON std::vector<std::uint8_t> v_bson = json::to_bson(j); // 0x1B, 0x00, 0x00, 0x00, 0x08, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0x00, 0x01, 0x10, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 // roundtrip json j_from_bson = json::from_bson(v_bson); // serialize to CBOR std::vector<std::uint8_t> v_cbor = json::to_cbor(j); // 0xA2, 0x67, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xF5, 0x66, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00 // roundtrip json j_from_cbor = json::from_cbor(v_cbor); // serialize to MessagePack std::vector<std::uint8_t> v_msgpack = json::to_msgpack(j); // 0x82, 0xA7, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xC3, 0xA6, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00 // roundtrip json j_from_msgpack = json::from_msgpack(v_msgpack); // serialize to UBJSON std::vector<std::uint8_t> v_ubjson = json::to_ubjson(j); // 0x7B, 0x69, 0x07, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0x54, 0x69, 0x06, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x69, 0x00, 0x7D // roundtrip json j_from_ubjson = json::from_ubjson(v_ubjson); // serialize to BON8 std::vector<std::uint8_t> v_bon8 = json::to_bon8(j); // 0x88, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xF9, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x90 // roundtrip json j_from_bon8 = json::from_bon8(v_bon8); ``` The library also supports binary types from BSON, CBOR (byte strings), and MessagePack (bin, ext, fixext). They are stored by default as `std::vector<std::uint8_t>` to be processed outside the library. ```cpp // CBOR byte string with payload 0xCAFE std::vector<std::uint8_t> v = {0x42, 0xCA, 0xFE}; // read value json j = json::from_cbor(v); // the JSON value has type binary j.is_binary(); // true // get reference to stored binary value auto& binary = j.get_binary(); // the binary value has no subtype (CBOR has no binary subtypes) binary.has_subtype(); // false // access std::vector<std::uint8_t> member functions binary.size(); // 2 binary[0]; // 0xCA binary[1]; // 0xFE // set subtype to 0x10 binary.set_subtype(0x10); // serialize to MessagePack auto msgpack = json::to_msgpack(j); // 0xD5 (fixext2), 0x10, 0xCA, 0xFE ``` ## Customers The library is used in multiple projects, applications, operating systems, etc. The list below is not exhaustive, but the result of an internet search. If you know further customers of the library, please let me know, see [contact](#contact). [](https://json.nlohmann.me/home/customers/) ## Ecosystem Beyond projects that use the library, there are third-party projects that build on top of it - schema validators, language bindings, format converters, and the like. See the curated [Ecosystem](https://json.nlohmann.me/community/ecosystem/) page. ## Supported compilers Though it's 2026 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work: - GCC 4.8 - 16.2 (and possibly later) - Clang 3.4 - 22.1 (and possibly later) - Apple Clang 15.0 - 21.0 (and possibly later) - Intel C++ Compiler Classic (icpc) 2021.10 - Intel oneAPI DPC++/C++ Compiler (icpx) 2025.3 (and possibly later) - NVIDIA CUDA Compiler (nvcc) 11.8 - 12.6 (and possibly later) - NVIDIA HPC SDK C++ Compiler (nvc++) 25.5 (and possibly later) - Microsoft Visual C++ 2015 / MSVC 19.0 (and possibly later) - Microsoft Visual C++ 2017 / MSVC 19.16 (and possibly later) - Microsoft Visual C++ 2019 / MSVC 19.29 (and possibly later) - Microsoft Visual C++ 2022 / MSVC 19.44 (and possibly later) - Microsoft Visual C++ 2026 / MSVC 19.51 (and possibly later) I would be happy to learn about other compilers/versions. Please note: - GCC 4.8 has a bug [57824](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57824): multiline raw strings cannot be the arguments to macros. Don't use multiline raw strings directly in macros with this compiler. - For GCC running on MinGW or Android, the error `'to_string' is not a member of 'std'` (or similarly, for `strtod` or `strtof`) may occur. Note this is not an issue with the code, but rather with the compiler or C++ standard library itself: use a recent toolchain (for Android, a current [NDK](https://developer.android.com/ndk) with the LLVM C++ library `APP_STL := c++_shared`, and for MinGW, a distribution with a complete C++11 standard library). See [this discussion](https://github.com/nlohmann/json/issues/136) for MinGW and [this discussion](https://github.com/nlohmann/json/issues/219) for the old Android NDK using `APP_STL := gnustl_static`. - Unsupported versions of GCC and Clang are rejected by `#error` directives. This can be switched off by defining `JSON_SKIP_UNSUPPORTED_COMPILER_CHECK`. Note that you can expect no support in this case. See the page [quality assurance](https://json.nlohmann.me/community/quality_assurance) on the compilers used to check the library in the CI. ## Integration [`json.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp) is the single required file in `single_include/nlohmann` or [released here](https://github.com/nlohmann/json/releases). You need to add ```cpp #include <nlohmann/json.hpp> // for convenience using json = nlohmann::json; ``` to the files you want to process JSON and set the necessary switches to enable C++11 (e.g., `-std=c++11` for GCC and Clang). You can further use file [`include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/json_fwd.hpp) for forward-declarations. The installation of `json_fwd.hpp` (as part of cmake's install step) can be achieved by setting `-DJSON_MultipleHeaders=ON`. ### CMake You can also use the `nlohmann_json::nlohmann_json` interface target in CMake. This target populates the appropriate usage requirements for `INTERFACE_INCLUDE_DIRECTORIES` to point to the appropriate include directories and `INTERFACE_COMPILE_FEATURES` for the necessary C++11 flags. #### External To use this library from a CMake project, you can locate it directly with `find_package()` and use the namespaced imported target from the generated package configuration: ```cmake # CMakeLists.txt find_package(nlohmann_json 3.12.0 REQUIRED) ... add_library(foo ...) ... target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json) ``` The package configuration file, `nlohmann_jsonConfig.cmake`, can be used either from an install tree or directly out of the build tree. #### Embedded To embed the library directly into an existing CMake project, place the entire source tree in a subdirectory and call `add_subdirectory()` in your `CMakeLists.txt` file: ```cmake # Typically you don't care so much for a third party library's tests to be # run from your own project's code. set(JSON_BuildTests OFF CACHE INTERNAL "") # If you only include this third party in PRIVATE source files, you do not # need to install it when your main project gets installed. # set(JSON_Install OFF CACHE INTERNAL "") # Don't use include(nlohmann_json/CMakeLists.txt) since that carries with it # unintended consequences that will break the build. It's generally # discouraged (although not necessarily well documented as such) to use # include(...) for pulling in other CMake projects anyways. add_subdirectory(nlohmann_json) ... add_library(foo ...) ... target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json) ``` ##### Embedded (FetchContent) Since CMake v3.11, [FetchContent](https://cmake.org/cmake/help/v3.11/module/FetchContent.html) can be used to automatically download a release as a dependency at configure time. Example: ```cmake include(FetchContent) FetchContent_Declare(json URL https://github.com/nlohmann/json/releases/download/v3.12.0/json.tar.xz) FetchContent_MakeAvailable(json) target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json) ``` **Note**: It is recommended to use the URL approach described above, which is supported as of version 3.10.0. See <https://json.nlohmann.me/integration/cmake/#fetchcontent> for more information. #### Supporting Both To allow your project to support either an externally supplied or an embedded JSON library, you can use a pattern akin to the following: ``` cmake # Top level CMakeLists.txt project(FOO) ... option(FOO_USE_EXTERNAL_JSON "Use an external JSON library" OFF) ... add_subdirectory(thirdparty) ... add_library(foo ...) ... # Note that the namespaced target will always be available regardless of the # import method target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json) ``` ```cmake # thirdparty/CMakeLists.txt ... if(FOO_USE_EXTERNAL_JSON) find_package(nlohmann_json 3.12.0 REQUIRED) else() set(JSON_BuildTests OFF CACHE INTERNAL "") add_subdirectory(nlohmann_json) endif() ... ``` `thirdparty/nlohmann_json` is then a complete copy of this source tree. ### Package Managers Use your favorite [**package manager**](https://json.nlohmann.me/integration/package_managers/) to use the library. - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/homebrew.svg" height="20"> [**Homebrew**](https://json.nlohmann.me/integration/package_managers/#homebrew) `nlohmann-json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/meson.svg" height="20"> [**Meson**](https://json.nlohmann.me/integration/package_managers/#meson) `nlohmann_json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/bazel.svg" height="20"> [**Bazel**](https://json.nlohmann.me/integration/package_managers/#bazel) `nlohmann_json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/conan.svg" height="20"> [**Conan**](https://json.nlohmann.me/integration/package_managers/#conan) `nlohmann_json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/spack.svg" height="20"> [**Spack**](https://json.nlohmann.me/integration/package_managers/#spack) `nlohmann-json` - [**Hunter**](https://json.nlohmann.me/integration/package_managers/#hunter) `nlohmann_json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/vcpkg.png" height="20"> [**vcpkg**](https://json.nlohmann.me/integration/package_managers/#vcpkg) `nlohmann-json` - [**cget**](https://json.nlohmann.me/integration/package_managers/#cget) `nlohmann/json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/swift.svg" height="20"> [**Swift Package Manager**](https://json.nlohmann.me/integration/package_managers/#swift-package-manager) `nlohmann/json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/nuget.svg" height="20"> [**Nuget**](https://json.nlohmann.me/integration/package_managers/#nuget) `nlohmann.json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/conda.svg" height="20"> [**Conda**](https://json.nlohmann.me/integration/package_managers/#conda) `nlohmann_json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/macports.svg" height="20"> [**MacPorts**](https://json.nlohmann.me/integration/package_managers/#macports) `nlohmann-json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/CPM.png" height="20"> [**cpm.cmake**](https://json.nlohmann.me/integration/package_managers/#cpmcmake) `gh:nlohmann/json` - <img src="https://raw.githubusercontent.com/nlohmann/json/refs/heads/develop/docs/mkdocs/docs/images/package_managers/xmake.svg" height="20"> [**xmake**](https://json.nlohmann.me/integration/package_managers/#xmake) `nlohmann_json` The library is part of many package managers. See the [**documentation**](https://json.nlohmann.me/integration/package_managers/) for detailed descriptions and examples. ### Pkg-config If you are using bare Makefiles, you can use `pkg-config` to generate the include flags that point to where the library is installed: ```sh pkg-config nlohmann_json --cflags ``` ## License <img align="right" src="https://149753425.v2.pressablecdn.com/wp-content/uploads/2009/06/OSIApproved_100X125.png" alt="OSI approved license"> The class is licensed under the [MIT License](https://opensource.org/licenses/MIT): Copyright © 2013-2026 [Niels Lohmann](https://nlohmann.me) Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. * * * - The class contains the UTF-8 Decoder from Bjoern Hoehrmann which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright © 2008-2009 [Björn Hoehrmann](https://bjoern.hoehrmann.de/) <bjoern@hoehrmann.de> - The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright © 2009 [Florian Loitsch](https://florian.loitsch.com/) - The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/). - The class contains parts of [Google Abseil](https://github.com/abseil/abseil-cpp) which is licensed under the [Apache 2.0 License](https://opensource.org/licenses/Apache-2.0). - The class contains an adapted version of the Eisel-Lemire algorithm and its table of powers of five from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright © 2021 The fast_float authors <img align="right" src="https://git.fsfe.org/reuse/reuse-ci/raw/branch/master/reuse-horizontal.png" alt="REUSE Software"> The library is compliant to version 3.3 of the [**REUSE specification**](https://reuse.software): - Every source file contains an SPDX copyright header. - The full text of all licenses used in the repository can be found in the `LICENSES` folder. - File `REUSE.toml` contains an overview of all files' copyrights and licenses. - Run `pipx run reuse lint` to verify the project's REUSE compliance and `pipx run reuse spdx` to generate a SPDX SBOM. ## Contact If you have questions regarding the library, I would like to invite you to [open an issue at GitHub](https://github.com/nlohmann/json/issues/new/choose). Please describe your request, problem, or question as detailed as possible, and also mention the version of the library you are using as well as the version of your compiler and operating system. Opening an issue at GitHub allows other users and contributors to this library to collaborate. For instance, I have little experience with MSVC, and most issues in this regard have been solved by a growing community. If you have a look at the [closed issues](https://github.com/nlohmann/json/issues?q=is%3Aissue+is%3Aclosed), you will see that we react quite timely in most cases. Only if your request would contain confidential information, please [send me an email](mailto:mail@nlohmann.me). For encrypted messages, please use [this key](https://keybase.io/nlohmann/pgp_keys.asc). ## Security [Commits by Niels Lohmann](https://github.com/nlohmann/json/commits) and [releases](https://github.com/nlohmann/json/releases) are signed with this [PGP Key](https://keybase.io/nlohmann/pgp_keys.asc?fingerprint=797167ae41c0a6d9232e48457f3cea63ae251b69). ## Thanks I deeply appreciate the help of the following people. <img src="https://raw.githubusercontent.com/nlohmann/json/develop/docs/avatars.png" align="right" alt="GitHub avatars of the contributors"> 1. [Teemperor](https://github.com/Teemperor) implemented CMake support and lcov integration, realized escape and Unicode handling in the string parser, and fixed the JSON serialization. 2. [elliotgoodrich](https://github.com/elliotgoodrich) fixed an issue with double deletion in the iterator classes. 3. [kirkshoop](https://github.com/kirkshoop) made the iterators of the class composable to other libraries. 4. [wancw](https://github.com/wanwc) fixed a bug that hindered the class to compile with Clang. 5. Tomas Åblad found a bug in the iterator implementation. 6. [Joshua C. Randall](https://github.com/jrandall) fixed a bug in the floating-point serialization. 7. [Aaron Burghardt](https://github.com/aburgh) implemented code to parse streams incrementally. Furthermore, he greatly improved the parser class by allowing the definition of a filter function to discard undesired elements while parsing. 8. [Daniel Kopeček](https://github.com/dkopecek) fixed a bug in the compilation with GCC 5.0. 9. [Fiona Johanna Weber](https://github.com/Fiona-J-W) fixed a bug in and improved the performance of the comparison operators. 10. [Eric Cornelius](https://github.com/EricMCornelius) pointed out a bug in the handling with NaN and infinity values. He also improved the performance of the string escaping. 11. [易思龙](https://github.com/likebeta) implemented a conversion from anonymous enums. 12. [kepkin](https://github.com/kepkin) patiently pushed forward the support for Microsoft Visual Studio. 13. [gregmarr](https://github.com/gregmarr) simplified the implementation of reverse iterators and helped with numerous hints and improvements. In particular, he pushed forward the implementation of user-defined types. 14. [Caio Luppi](https://github.com/caiovlp) fixed a bug in the Unicode handling. 15. [dariomt](https://github.com/dariomt) fixed some typos in the examples and fixed a subtlety in MSVC type support and implemented the `get_ref()` function to get a reference to stored values. 16. [Daniel Frey](https://github.com/d-frey) cleaned up some pointers and implemented exception-safe memory allocation. 17. [Colin Hirsch](https://github.com/ColinH) took care of a small namespace issue. 18. [Huu Nguyen](https://github.com/whoshuu) corrected a variable name in the documentation. 19. [Silverweed](https://github.com/silverweed) overloaded `parse()` to accept an rvalue reference. 20. [ZahlGraf](https://github.com/ZahlGraf) added a workaround that allows compilation using Android NDK. 21. [whackashoe](https://github.com/whackashoe) replaced a function that was marked as unsafe by Visual Studio. 22. [406345](https://github.com/406345) fixed two small warnings. 23. [Glen Fernandes](https://github.com/glenfe) noted a potential portability problem in the `has_mapped_type` function. 24. [Corbin Hughes](https://github.com/nibroc) fixed some typos in the contribution guidelines. 25. [twelsby](https://github.com/twelsby) fixed the array subscript operator, an issue that failed the MSVC build, and floating-point parsing/dumping. He further added support for unsigned integer numbers and implemented better roundtrip support for parsed numbers. 26. [Volker Diels-Grabsch](https://github.com/vog) fixed a link in the README file. 27. [msm-](https://github.com/msm-) added support for American Fuzzy Lop. 28. [Annihil](https://github.com/Annihil) fixed an example in the README file. 29. [Themercee](https://github.com/Themercee) noted a wrong URL in the README file. 30. [Lv Zheng](https://github.com/lv-zheng) fixed a namespace issue with `int64_t` and `uint64_t`. 31. [abc100m](https://github.com/abc100m) analyzed the issues with GCC 4.8 and proposed a [partial solution](https://github.com/nlohmann/json/pull/212). 32. [zewt](https://github.com/zewt) added useful notes to the README file about Android. 33. [Róbert Márki](https://github.com/robertmrk) added a fix to use move iterators and improved the integration via CMake. 34. [Chris Kitching](https://github.com/ChrisKitching) cleaned up the CMake files. 35. [Tom Needham](https://github.com/06needhamt) fixed a subtle bug with MSVC 2015 which was also proposed by [Michael K.](https://github.com/Epidal). 36. [Mário Feroldi](https://github.com/thelostt) fixed a small typo. 37. [duncanwerner](https://github.com/duncanwerner) found a really embarrassing performance regression in the 2.0.0 release. 38. [Damien](https://github.com/dtoma) fixed one of the last conversion warnings. 39. [Thomas Braun](https://github.com/t-b) fixed a warning in a test case and adjusted MSVC calls in the CI. 40. [Théo DELRIEU](https://github.com/theodelrieu) patiently and constructively oversaw the long way toward [iterator-range parsing](https://github.com/nlohmann/json/issues/290). He also implemented the magic behind the serialization/deserialization of user-defined types and split the single header file into smaller chunks. 41. [Stefan](https://github.com/5tefan) fixed a minor issue in the documentation. 42. [Vasil Dimov](https://github.com/vasild) fixed the documentation regarding conversions from `std::multiset`. 43. [ChristophJud](https://github.com/ChristophJud) overworked the CMake files to ease project inclusion. 44. [Vladimir Petrigo](https://github.com/vpetrigo) made a SFINAE hack more readable and added Visual Studio 17 to the build matrix. 45. [Denis Andrejew](https://github.com/seeekr) fixed a grammar issue in the README file. 46. [Pierre-Antoine Lacaze](https://github.com/palacaze) found a subtle bug in the `dump()` function. 47. [TurpentineDistillery](https://github.com/TurpentineDistillery) pointed to [`std::locale::classic()`](https://en.cppreference.com/w/cpp/locale/locale/classic) to avoid too much locale joggling, found some nice performance improvements in the parser, improved the benchmarking code, and realized locale-independent number parsing and printing. 48. [cgzones](https://github.com/cgzones) had an idea how to fix the Coverity scan. 49. [Jared Grubb](https://github.com/jaredgrubb) silenced a nasty documentation warning and supported the implementation of user-defined types. 50. [Yixin Zhang](https://github.com/qwename) fixed an integer overflow check. 51. [Bosswestfalen](https://github.com/Bosswestfalen) merged two iterator classes into a smaller one. 52. [Daniel599](https://github.com/Daniel599) helped to get Travis to execute the tests with Clang's sanitizers and allowed to use more algorithms with the `items()` function. 53. [Jonathan Lee](https://github.com/vjon) fixed an example in the README file. 54. [gnzlbg](https://github.com/gnzlbg) supported the implementation of user-defined types. 55. [Alexej Harm](https://github.com/qis) helped to get the user-defined types working with Visual Studio. 56. [EnricoBilla](https://github.com/EnricoBilla) noted a typo in an example. 57. [Martin Hořeňovský](https://github.com/horenmar) found a way for a 2x speedup for the compilation time of the test suite. 58. [ukhegg](https://github.com/ukhegg) proposed an improvement for the examples section. 59. [rswanson-ihi](https://github.com/rswanson-ihi) noted a typo in the README. 60. [Mihai Stan](https://github.com/stanmihai4) fixed a bug in the comparison with `nullptr`s. 61. [Tushar Maheshwari](https://github.com/tusharpm) added [cotire](https://github.com/sakra/cotire) support to speed up the compilation. 62. [TedLyngmo](https://github.com/TedLyngmo) noted a typo in the README, removed unnecessary bit arithmetic, and fixed some `-Weffc++` warnings. 63. [Krzysztof Woś](https://github.com/krzysztofwos) made exceptions more visible. 64. [ftillier](https://github.com/ftillier) fixed a compiler warning. 65. [tinloaf](https://github.com/tinloaf) made sure all pushed warnings are properly popped. 66. [Fytch](https://github.com/Fytch) found a bug in the documentation. 67. [Jay Sistar](https://github.com/Type1J) implemented a Meson build description. 68. [Henry Lee](https://github.com/HenryRLee) fixed a warning in ICC and improved the iterator implementation. 69. [Vincent Thiery](https://github.com/vthiery) maintains a package for the Conan package manager. 70. [Steffen](https://github.com/koemeet) fixed a potential issue with MSVC and `std::min`. 71. [Mike Tzou](https://github.com/Chocobo1) fixed some typos. 72. [amrcode](https://github.com/amrcode) noted misleading documentation about comparison of floats. 73. [Oleg Endo](https://github.com/olegendo) reduced the memory consumption by replacing `<iostream>` with `<iosfwd>`. 74. [dan-42](https://github.com/dan-42) cleaned up the CMake files to simplify including/reusing of the library. 75. [Nikita Ofitserov](https://github.com/himikof) allowed for moving values from initializer lists. 76. [Greg Hurrell](https://github.com/wincent) fixed a typo. 77. [Dmitry Kukovinets](https://github.com/DmitryKuk) fixed a typo. 78. [kbthomp1](https://github.com/kbthomp1) fixed an issue related to the Intel OSX compiler. 79. [Markus Werle](https://github.com/daixtrose) fixed a typo. 80. [WebProdPP](https://github.com/WebProdPP) fixed a subtle error in a precondition check. 81. [Alex](https://github.com/leha-bot) noted an error in a code sample. 82. [Tom de Geus](https://github.com/tdegeus) reported some warnings with ICC and helped to fix them. 83. [Perry Kundert](https://github.com/pjkundert) simplified reading from input streams. 84. [Sonu Lohani](https://github.com/sonulohani) fixed a small compilation error, fixed the compilation with MSVC 2015 in debug mode and fixed a warning. 85. [Jamie Seward](https://github.com/jseward) fixed all MSVC warnings and avoided unnecessary string copies in `find()` and `count()`. 86. [Nate Vargas](https://github.com/eld00d) added a Doxygen tag file. 87. [pvleuven](https://github.com/pvleuven) helped to fix a warning in ICC. 88. [Pavel](https://github.com/crea7or) helped to fix some warnings in MSVC. 89. [Mitja](https://github.com/Itja) fixed some typos. 90. [Jorrit Wronski](https://github.com/jowr) updated the Hunter package links. 91. [Matthias Möller](https://github.com/TinyTinni) added a `.natvis` for the MSVC debug view and removed the dependency from `std::stringstream`. 92. [bogemic](https://github.com/bogemic) fixed some C++17 deprecation warnings. 93. [Eren Okka](https://github.com/erengy) fixed some MSVC warnings. 94. [abolz](https://github.com/abolz) integrated the Grisu2 algorithm for proper floating-point formatting, allowing more roundtrip checks to succeed. 95. [Vadim Evard](https://github.com/Pipeliner) fixed a Markdown issue in the README. 96. [zerodefect](https://github.com/zerodefect) fixed a compiler warning. 97. [Kert](https://github.com/kaidokert) allowed to template the string type in the serialization and added the possibility to override the exceptional behavior. 98. [mark-99](https://github.com/mark-99) helped fix an ICC error. 99. [Patrik Huber](https://github.com/patrikhuber) fixed links in the README file. 100. [johnfb](https://github.com/johnfb) found a bug in the implementation of CBOR's indefinite length strings. 101. [Paul Fultz II](https://github.com/pfultz2) added a note on the cget package manager. 102. [Wilson Lin](https://github.com/wla80) made the integration section of the README more concise. 103. [RalfBielig](https://github.com/ralfbielig) detected and fixed a memory leak in the parser callback. 104. [agrianius](https://github.com/agrianius) allowed dumping JSON to an alternative string type and added code to use alternative string implementations. 105. [Kevin Tonon](https://github.com/ktonon) overworked the C++11 compiler checks in CMake. 106. [Axel Huebl](https://github.com/ax3l) simplified a CMake check and added support for the [Spack package manager](https://spack.io). 107. [Carlos O'Ryan](https://github.com/coryan) fixed a typo. 108. [James Upjohn](https://github.com/jupjohn) fixed a version number in the compilers section. 109. [Chuck Atkins](https://github.com/chuckatkins) adjusted the CMake files to the CMake packaging guidelines and provided documentation for the CMake integration. 110. [Jan Schöppach](https://github.com/dns13) fixed a typo. 111. [martin-mfg](https://github.com/martin-mfg) fixed a typo. 112. [Julius Rakow](https://github.com/juliusrakow) fixed the Meson include directory and fixed the links to [cppreference.com](https://cppreference.com). 113. [grembo](https://github.com/grembo) fixed the test suite and re-enabled several test cases. 114. [Hyeon Kim](https://github.com/simnalamburt) introduced the macro `JSON_INTERNAL_CATCH` to control the exception handling inside the library and fixed an issue with a double macro definition. 115. [thyu](https://github.com/thyu) fixed a compiler warning. 116. [David Guthrie](https://github.com/LEgregius) fixed a subtle compilation error with Clang 3.4.2. 117. [Dennis Fischer](https://github.com/dennisfischer) allowed to call `find_package` without installing the library. 118. [Ben Berman](https://github.com/rivertam) made some error messages more understandable. 119. [zakalibit](https://github.com/zakalibit) fixed a compilation problem with the Intel C++ compiler. 120. [mandreyel](https://github.com/mandreyel) fixed a compilation problem. 121. [Kostiantyn Ponomarenko](https://github.com/koponomarenko) added version and license information to the Meson build file. 122. [Henry Schreiner](https://github.com/henryiii) added support for GCC 4.8. 123. [knilch](https://github.com/knilch0r) made sure the test suite does not stall when run in the wrong directory. 124. [Antonio Borondo](https://github.com/antonioborondo) fixed an MSVC 2017 warning. 125. [Dan Gendreau](https://github.com/dgendreau) implemented the `NLOHMANN_JSON_SERIALIZE_ENUM` macro to quickly define an enum/JSON mapping. 126. [efp](https://github.com/efp) added line and column information to parse errors. 127. [julian-becker](https://github.com/julian-becker) added BSON support. 128. [Pratik Chowdhury](https://github.com/pratikpc) added support for structured bindings. 129. [David Avedissian](https://github.com/davedissian) added support for Clang 5.0.1 (PS4 version). 130. [Jonathan Dumaresq](https://github.com/dumarjo) implemented an input adapter to read from `FILE*`. 131. [kjpus](https://github.com/kjpus) fixed a link in the documentation. 132. [Manvendra Singh](https://github.com/manu-chroma) fixed a typo in the documentation. 133. [ziggurat29](https://github.com/ziggurat29) fixed an MSVC warning. 134. [Sylvain Corlay](https://github.com/SylvainCorlay) added code to avoid an issue with MSVC. 135. [mefyl](https://github.com/mefyl) fixed a bug when JSON was parsed from an input stream. 136. [Millian Poquet](https://github.com/mpoquet) allowed to install the library via Meson. 137. [Michael Behrns-Miller](https://github.com/moodboom) found an issue with a missing namespace. 138. [Nasztanovics Ferenc](https://github.com/naszta) fixed a compilation issue with libc 2.12. 139. [Andreas Schwab](https://github.com/andreas-schwab) fixed the endian conversion. 140. [Mark-Dunning](https://github.com/Mark-Dunning) fixed a warning in MSVC. 141. [Gareth Sylvester-Bradley](https://github.com/garethsb-sony) added `operator/` for JSON Pointers and fixed a compilation issue with MSVC. 142. [John-Mark](https://github.com/johnmarkwayve) noted a missing header. 143. [Vitaly Zaitsev](https://github.com/xvitaly) fixed compilation with GCC 9.0. 144. [Laurent Stacul](https://github.com/stac47) fixed compilation with GCC 9.0. 145. [Ivor Wanders](https://github.com/iwanders) helped to reduce the CMake requirement to version 3.1 and fixed the examples to catch exception by `const&`. 146. [njlr](https://github.com/njlr) updated the Buckaroo instructions. 147. [Lion](https://github.com/lieff) fixed a compilation issue with GCC 7 on CentOS. 148. [Isaac Nickaein](https://github.com/nickaein) improved the integer serialization performance and implemented the `contains()` function. 149. [past-due](https://github.com/past-due) suppressed an unfixable warning. 150. [Elvis Oric](https://github.com/elvisoric) improved Meson support. 151. [Matěj Plch](https://github.com/Afforix) fixed an example in the README. 152. [Mark Beckwith](https://github.com/wythe) fixed two typos. 153. [scinart](https://github.com/scinart) fixed a bug in the serializer. 154. [Patrick Boettcher](https://github.com/pboettch) implemented `push_back()` and `pop_back()` for JSON Pointers. 155. [Bruno Oliveira](https://github.com/nicoddemus) added support for Conda. 156. [Michele Caini](https://github.com/skypjack) fixed links in the README. 157. [Hani](https://github.com/hnkb) documented how to install the library with NuGet. 158. [yann-morin-1998](https://github.com/yann-morin-1998) helped to reduce the CMake requirement to version 3.1. 159. [Konstantin Podsvirov](https://github.com/podsvirov) maintains a package for the MSYS2 software distro and fixed the MSYS2 package documentation. 160. [remyabel](https://github.com/remyabel2) added GNUInstallDirs to the CMake files. 161. [Taylor Howard](https://github.com/taylorhoward92) fixed a unit test. 162. [Gabe Ron](https://github.com/Macr0Nerd) implemented the `to_string` method. 163. [Watal M. Iwasaki](https://github.com/heavywatal) fixed a Clang warning. 164. [Viktor Kirilov](https://github.com/onqtam) switched the unit tests from [Catch](https://github.com/philsquared/Catch) to [doctest](https://github.com/doctest/doctest) 165. [Juncheng E](https://github.com/ejcjason) fixed a typo. 166. [tete17](https://github.com/tete17) fixed a bug in the `contains` function. 167. [Xav83](https://github.com/Xav83) fixed some cppcheck warnings. 168. [0xflotus](https://github.com/0xflotus) fixed some typos. 169. [Christian Deneke](https://github.com/chris0x44) added a const version of `json_pointer::back`. 170. [Julien Hamaide](https://github.com/crazyjul) made the `items()` function work with custom string types. 171. [Evan Nemerson](https://github.com/nemequ) updated fixed a bug in Hedley and updated this library accordingly. 172. [Florian Pigorsch](https://github.com/flopp) fixed a lot of typos. 173. [Camille Bégué](https://github.com/cbegue) fixed an issue in the conversion from `std::pair` and `std::tuple` to `json`. 174. [Anthony VH](https://github.com/AnthonyVH) fixed a compile error in an enum deserialization. 175. [Yuriy Vountesmery](https://github.com/ua-code-dragon) noted a subtle bug in a preprocessor check. 176. [Chen](https://github.com/dota17) fixed numerous issues in the library. 177. [Antony Kellermann](https://github.com/aokellermann) added a CI step for GCC 10.1. 178. [Alex](https://github.com/gistrec) fixed an MSVC warning. 179. [Rainer](https://github.com/rvjr) proposed an improvement in the floating-point serialization in CBOR. 180. [Francois Chabot](https://github.com/FrancoisChabot) made performance improvements in the input adapters. 181. [Arthur Sonzogni](https://github.com/ArthurSonzogni) documented how the library can be included via `FetchContent`. 182. [Rimas Misevičius](https://github.com/rmisev) fixed an error message. 183. [Alexander Myasnikov](https://github.com/alexandermyasnikov) fixed some examples and a link in the README. 184. [Hubert Chathi](https://github.com/uhoreg) made CMake's version config file architecture-independent. 185. [OmnipotentEntity](https://github.com/OmnipotentEntity) implemented the binary values for CBOR, MessagePack, BSON, and UBJSON. 186. [ArtemSarmini](https://github.com/ArtemSarmini) fixed a compilation issue with GCC 10 and fixed a leak. 187. [Evgenii Sopov](https://github.com/sea5kg) integrated the library to the wsjcpp package manager. 188. [Sergey Linev](https://github.com/linev) fixed a compiler warning. 189. [Miguel Magalhães](https://github.com/magamig) fixed the year in the copyright. 190. [Alexander “weej” Jones](https://github.com/alex-weej) fixed an example in the README. 191. [Antoine Cœur](https://github.com/Coeur) fixed some typos in the documentation. 192. [jothepro](https://github.com/jothepro) updated links to the Hunter package. 193. [Dave Lee](https://github.com/kastiglione) fixed a link in the README. 194. [Joël Lamotte](https://github.com/Klaim) added instruction for using Build2's package manager. 195. [Paul Jurczak](https://github.com/pauljurczak) fixed an example in the README. 196. [Carlos Gomes Martinho](https://github.com/gocarlos) updated the Conan package source. 197. [Tridacnid](https://github.com/Tridacnid) improved the CMake tests. 198. [Michael](https://github.com/MBalszun) fixed MSVC warnings. 199. [Quentin Barbarat](https://github.com/quentin-dev) fixed an example in the documentation. 200. [XyFreak](https://github.com/XyFreak) fixed a compiler warning. 201. [TotalCaesar659](https://github.com/TotalCaesar659) fixed links in the README and updated the links in the documentation to use HTTPS. 202. [Tanuj Garg](https://github.com/tanuj208) improved the fuzzer coverage for UBSAN input. 203. [AODQ](https://github.com/AODQ) fixed a compiler warning. 204. [jwittbrodt](https://github.com/jwittbrodt) made `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE` inline. 205. [pfeatherstone](https://github.com/pfeatherstone) improved the upper bound of arguments of the `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`/`NLOHMANN_DEFINE_TYPE_INTRUSIVE` macros. 206. [Jan Procházka](https://github.com/jprochazk) fixed a bug in the CBOR parser for binary and string values. 207. [T0b1-iOS](https://github.com/T0b1-iOS) fixed a bug in the new hash implementation. 208. [Matthew Bauer](https://github.com/matthewbauer) adjusted the CBOR writer to create tags for binary subtypes. 209. [gatopeich](https://github.com/gatopeich) implemented an ordered map container for `nlohmann::ordered_json`. 210. [Érico Nogueira Rolim](https://github.com/ericonr) added support for pkg-config. 211. [KonanM](https://github.com/KonanM) proposed an implementation for the `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`/`NLOHMANN_DEFINE_TYPE_INTRUSIVE` macros. 212. [Guillaume Racicot](https://github.com/gracicot) implemented `string_view` support and allowed C++20 support. 213. [Alex Reinking](https://github.com/alexreinking) improved CMake support for `FetchContent`. 214. [Hannes Domani](https://github.com/ssbssa) provided a GDB pretty printer. 215. Lars Wirzenius reviewed the README file. 216. [Jun Jie](https://github.com/ongjunjie) fixed a compiler path in the CMake scripts. 217. [Ronak Buch](https://github.com/rbuch) fixed typos in the documentation. 218. [Alexander Karzhenkov](https://github.com/karzhenkov) fixed a move constructor and the Travis builds. 219. [Leonardo Lima](https://github.com/leozz37) added CPM.Cmake support. 220. [Joseph Blackman](https://github.com/jbzdarkid) fixed a warning. 221. [Yaroslav](https://github.com/YarikTH) updated doctest and implemented unit tests. 222. [Martin Stump](https://github.com/globberwops) fixed a bug in the CMake files. 223. [Jaakko Moisio](https://github.com/jasujm) fixed a bug in the input adapters. 224. [bl-ue](https://github.com/bl-ue) fixed some Markdown issues in the README file. 225. [William A. Wieselquist](https://github.com/wawiesel) fixed an example from the README. 226. [abbaswasim](https://github.com/abbaswasim) fixed an example from the README. 227. [Remy Jette](https://github.com/remyjette) fixed a warning. 228. [Fraser](https://github.com/frasermarlow) fixed the documentation. 229. [Ben Beasley](https://github.com/musicinmybrain) updated doctest. 230. [Doron Behar](https://github.com/doronbehar) fixed pkg-config.pc. 231. [raduteo](https://github.com/raduteo) fixed a warning. 232. [David Pfahler](https://github.com/theShmoo) added the possibility to compile the library without I/O support. 233. [Morten Fyhn Amundsen](https://github.com/mortenfyhn) fixed a typo. 234. [jpl-mac](https://github.com/jpl-mac) allowed treating the library as a system header in CMake. 235. [Jason Dsouza](https://github.com/jasmcaus) fixed the indentation of the CMake file. 236. [offa](https://github.com/offa) added a link to Conan Center to the documentation. 237. [Rafail Giavrimis](https://github.com/grafail) fixed the Google Benchmark default branch. 238. [Louis Dionne](https://github.com/ldionne) fixed a conversion operator. 239. [justanotheranonymoususer](https://github.com/justanotheranonymoususer) made the examples in the README more consistent. 240. [Finkman](https://github.com/Finkman) suppressed some `-Wfloat-equal` warnings and fixed the debug pretty-printer. 241. [Ferry Huberts](https://github.com/fhuberts) fixed `-Wswitch-enum` warnings and fixed a typo. 242. [Arseniy Terekhin](https://github.com/senyai) made the GDB pretty-printer robust against unset variable names. 243. [Amir Masoud Abdol](https://github.com/amirmasoudabdol) updated the Homebrew command as nlohmann/json is now in homebrew-core. 244. [Hallot](https://github.com/Hallot) fixed some `-Wextra-semi-stmt warnings`. 245. [Giovanni Cerretani](https://github.com/gcerretani) fixed `-Wunused` warnings on `JSON_DIAGNOSTICS` and fixed a check for `std::filesystem`. 246. [Bogdan Popescu](https://github.com/Kapeli) hosts the [docset](https://github.com/Kapeli/Dash-User-Contributions/tree/master/docsets/JSON_for_Modern_C%2B%2B) for offline documentation viewers. 247. [Carl Smedstad](https://github.com/carlsmedstad) fixed an assertion error when using `JSON_DIAGNOSTICS`. 248. [miikka75](https://github.com/miikka75) provided an important fix to compile C++17 code with Clang 9. 249. [Maarten Becker](https://github.com/kernie) fixed a warning for shadowed variables. 250. [Cristi Vîjdea](https://github.com/axnsan12) fixed typos in the `operator[]` documentation. 251. [Alex Beregszaszi](https://github.com/axic) fixed spelling mistakes in comments. 252. [Dirk Stolle](https://github.com/striezel) fixed typos in the documentation. 253. [Daniel Albuschat](https://github.com/daniel-kun) corrected the parameter name in the `parse` documentation. 254. [Prince Mendiratta](https://github.com/Prince-Mendiratta) fixed a link to the FAQ. 255. [Florian Albrechtskirchinger](https://github.com/falbrechtskirchinger) implemented `std::string_view` support for object keys and made dozens of other improvements. 256. [Qianqian Fang](https://github.com/fangq) implemented the Binary JData (BJData) format. 257. [pketelsen](https://github.com/pketelsen) added macros `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT` and `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT`. 258. [DarkZeros](https://github.com/DarkZeros) adjusted to code to not clash with Arduino defines. 259. [flagarde](https://github.com/flagarde) fixed the output of `meta()` for MSVC. 260. [Dimitris Apostolou](https://github.com/rex4539) fixed a typo. 261. [Michael Nosthoff](https://github.com/heinemml) fixed a typo. 262. [JungHoon Lee](https://github.com/jhnlee) fixed a typo. 263. [Faruk D.](https://github.com/fdiblen) fixed the CITATION.CFF file. 264. [Andrea Cocito](https://github.com/puffetto) added a clarification on macro usage to the documentation. 265. [Krzysiek Karbowiak](https://github.com/kkarbowiak) refactored the tests to use `CHECK_THROWS_WITH_AS`. 266. [Chaoqi Zhang](https://github.com/prncoprs) fixed a typo. 267. [ivanovmp](https://github.com/ivanovmp) fixed a whitespace error. 268. [KsaNL](https://github.com/KsaNL) fixed a build error when including `<windows.h>`. 269. [Andrea Pappacoda](https://github.com/Tachi107) moved `.pc` and `.cmake` files to `share` directory. 270. [Wolf Vollprecht](https://github.com/wolfv) added the `patch_inplace` function. 271. [Jake Zimmerman](https://github.com/jez) highlighted common usage patterns in the README file. 272. [NN](https://github.com/NN---) added the Visual Studio output directory to `.gitignore`. 273. [Romain Reignier](https://github.com/romainreignier) improved the performance of the vector output adapter. 274. [Mike](https://github.com/Mike-Leo-Smith) fixed the `std::iterator_traits`. 275. [Richard Hozák](https://github.com/richardhozak) added macro `JSON_NO_ENUM` to disable default enum conversions. 276. [vakokako](https://github.com/vakokako) fixed tests when compiling with C++20. 277. [Alexander “weej” Jones](https://github.com/alexweej) fixed an example in the README. 278. [Eli Schwartz](https://github.com/eli-schwartz) added more files to the `include.zip` archive. 279. [Kevin Lu](https://github.com/kevinlul) fixed a compilation issue when typedefs with certain names were present. 280. [Trevor Hickey](https://github.com/luxe) improved the description of an example. 281. [Jef LeCompte](https://github.com/jef) updated the year in the README file. 282. [Alexandre Hamez](https://github.com/ahamez) fixed a warning. 283. [Maninderpal Badhan](https://github.com/mbadhan) fixed a typo. 284. [kevin--](https://github.com/kevin--) added a note to an example in the README file. 285. [I](https://github.com/wx257osn2) fixed a typo. 286. [Gregorio Litenstein](https://github.com/Lord-Kamina) fixed the Clang detection. 287. [Andreas Smas](https://github.com/andoma) added a Doozer badge. 288. [WanCW](https://github.com/wancw) fixed the string conversion with Clang. 289. [zhaohuaxishi](https://github.com/zhaohuaxishi) fixed a Doxygen error. 290. [emvivre](https://github.com/emvivre) removed an invalid parameter from CMake. 291. [Tobias Hermann](https://github.com/Dobiasd) fixed a link in the README file. 292. [Michael](https://github.com/traits) fixed a warning. 293. [Ryan Mulder](https://github.com/ryanjmulder) added `ensure_ascii` to the `dump` function. 294. [Muri Nicanor](https://github.com/murinicanor) fixed the `sed` discovery in the Makefile. 295. [David Avedissian](https://github.com/dgavedissian) implemented SFINAE-friendly `iterator_traits`. 296. [AQNOUCH Mohammed](https://github.com/aqnouch) fixed a typo in the README. 297. [Gareth Sylvester-Bradley](https://github.com/garethsb) added `operator/=` and `operator/` to construct JSON pointers. 298. [Michael Macnair](https://github.com/mykter) added support for afl-fuzz testing. 299. [Berkus Decker](https://github.com/berkus) fixed a typo in the README. 300. [Illia Polishchuk](https://github.com/ilqvya) improved the CMake testing. 301. [Ikko Ashimine](https://github.com/eltociear) fixed two typos. 302. [Raphael Grimm](https://github.com/barcode) added the possibility to define a custom base class. 303. [tocic](https://github.com/tocic) fixed typos in the documentation. 304. [Vertexwahn](https://github.com/Vertexwahn) added Bazel build support. 305. [DavidKorczynski](https://github.com/DavidKorczynski) added a CIFuzz CI GitHub action. 306. [Florian Segginger](https://github.com/floriansegginger) bumped the years in the README. 307. [haadfida](https://github.com/haadfida) cleaned up the badges of used services. 308. [Arsen Arsenović](https://github.com/ArsenArsen) fixed a build error. 309. [theevilone45](https://github.com/theevilone45) fixed a typo in a CMake file. 310. [Sergei Trofimovich](https://github.com/trofi) fixed the custom allocator support. 311. [Joyce](https://github.com/joycebrum) fixed some security issues in the GitHub workflows. 312. [Nicolas Jakob](https://github.com/njakob) add vcpkg version badge. 313. [Tomerkm](https://github.com/Tomerkm) added tests. 314. [No.](https://github.com/tusooa) fixed the use of `get<>` calls. 315. [taro](https://github.com/tarolling) fixed a typo in the `CODEOWNERS` file. 316. [Felix Yan](https://github.com/felixonmars) fixed a typo in the README. 317. [HO-COOH](https://github.com/HO-COOH) fixed a parenthesis in the documentation. 318. [miny1233](https://github.com/miny1233) fixed a parenthesis in the documentation. 319. [tomalakgeretkal](https://github.com/tomalakgeretkal) fixed a compilation error. 320. [alferov](https://github.com/ALF-ONE) fixed a compilation error and fixed a version in the documentation. 321. [Craig Scott](https://github.com/craigscott-crascit) fixed a deprecation warning in CMake. 322. [Vyacheslav Zhdanovskiy](https://github.com/ZeronSix) added macros for serialization-only types. 323. [Mathieu Westphal](https://github.com/mwestphal) fixed typos. 324. [scribam](https://github.com/scribam) fixed the MinGW workflow. 325. [Aleksei Sapitskii](https://github.com/aleksproger) added support for Apple's Swift Package Manager. 326. [Benjamin Buch](https://github.com/bebuch) fixed the installation path in CMake. 327. [Colby Haskell](https://github.com/colbychaskell) clarified the parse error message in case a file cannot be opened. 328. [Juan Carlos Arevalo Baeza](https://github.com/TheJCAB) fixed the enum conversion. 329. [ss](https://github.com/serge-s) fixed the amalgamation call. 330. [AniketDhemare](https://github.com/AniketDhemare) fixed a version in the documentation. 331. [Philip Müller](https://github.com/philip-paul-mueller) fixed an example. 332. [Leila Shcheglova](https://github.com/LeilaShcheglova) fixed a warning in a test. 333. [Alex Prabhat Bara](https://github.com/alexprabhat99) fixed a function name in the documentation. 334. [laterlaugh](https://github.com/laterlaugh) fixed some typos. 335. [Yuanhao Jia](https://github.com/MrJia1997) fixed the GDB pretty printer. 336. [Fallen_Breath](https://github.com/Fallen-Breath) fixed an example for JSON Pointer. 337. [Nikhil Idiculla](https://github.com/tsnl) fixed some typos. 338. [Griffin Myers](https://github.com/gmyers18) updated the Natvis file. 339. [thetimr](https://github.com/thetimr) fixed a typo in the documentation. 340. [Balazs Erseki](https://github.com/zerocukor287) fixed a URL in the contribution guidelines. 341. [Niccolò Iardella](https://github.com/rotolof) added `NLOHMANN_DEFINE_DERIVED_TYPE_*` macros. 342. [Borislav Stanimirov](https://github.com/iboB) allowed overriding the CMake target name. 343. [Captain Crutches](https://github.com/captaincrutches) made `iterator_proxy_value` a `std::forward_iterator`. 344. [Fredrik Sandhei](https://github.com/fsandhei) added type conversion support for `std::optional`. 345. [jh96](https://github.com/jordan-hoang) added exceptions when `nullptr` is passed to `parse`. 346. [Stuart Gorman](https://github.com/StuartGorman) fixed number parsing when `EINTR` set in `errno`. 347. [Dylan Baker](https://github.com/dcbaker) generated a pkg-config file that follows the pkg-config conventions. 348. [Tianyi Chen](https://github.com/TianyiChen) optimized the binary `get_number` implementation. 349. [peng-wang-cn](https://github.com/peng-wang-cn) added type conversion support for multidimensional arrays. 350. [Einars Netlis-Galejs](https://github.com/EinarsNG) added `ONLY_SERIALIZE` for `NLOHMANN_DEFINE_DERIVED_TYPE_*` macros. 351. [Marcel](https://github.com/mering) removed `alwayslink=True` Bazel flag. 352. [Harinath Nampally](https://github.com/hnampally) added diagnostic positions to exceptions. 353. [Nissim Armand Ben Danan](https://github.com/NissimBendanan) fixed `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT` with an empty JSON instance. 354. [Michael Valladolid](https://github.com/codenut) added support for BSON uint64 serialization/deserialization. 355. [Nikhil](https://github.com/nikhilreddydev) updated the documentation. 356. [Nebojša Cvetković](https://github.com/nebkat) added support for BJDATA optimized binary array type. 357. [Sushrut Shringarputale](https://github.com/sushshring) added support for diagnostic positions. 358. [kimci86](https://github.com/kimci86) templated to `NLOHMANN_DEFINE_TYPE` macros to also support `ordered_json`. 359. [Richard Topchii](https://github.com/richardtop) added support for VisionOS in the Swift Package Manager. 360. [Robert Chisholm](https://github.com/Robadob) fixed a typo. 361. [zjyhjqs](https://github.com/zjyhjqs) added CPack support. 362. [bitFiedler](https://github.com/bitFiedler) made GDB pretty printer work with Python 3.8. 363. [Gianfranco Costamagna](https://github.com/LocutusOfBorg) fixed a compiler warning. 364. [risa2000](https://github.com/risa2000) made `std::filesystem::path` conversion to/from UTF-8 encoded string explicit. 365. [AM](https://github.com/maqnouch) fixed typos in the README. 366. [dmenendez-gruposantander](https://github.com/dmenendez-gruposantander) fixed typos in the comments of the examples. 367. [Mihai Stan](https://github.com/mstan-xx) fixed comparisons against the literal `0`. 368. [Matt Gumbel](https://github.com/intelmatt) fixed some `-Weffc++` warnings. 369. [vimpunk](https://github.com/vimpunk) moved a lambda out of an unevaluated context to support older compilers. 370. [Chris Harris](https://github.com/cjh1) fixed the compilation with GCC 4.8. 371. [Palmer Dabbelt](https://github.com/palmer-dabbelt) generated and installed a pkg-config file. 372. [Gus Pozuelo](https://github.com/ap-viavi) made `ordered_map` compatible with GCC 5.5, Clang 3.6, and Xcode 9. 373. [AK](https://github.com/Lioncky) fixed an MSVC build error caused by the `min`/`max` macros from `windows.h`. 374. [Sergiu Deitsch](https://github.com/sergiud) provided a fallback for missing `char8_t` support. 375. [Xiaochuan Ye](https://github.com/XueSongTap) fixed `from_msgpack` for `std::byte` input by specializing `std::char_traits`. 376. [Ville Vesilehto](https://github.com/thevilledev) fixed an overflow in the BJData size calculation and rejected overflowing negative integers in CBOR. 377. [NmPassTHFan](https://github.com/nmpassthf) replaced the deprecated `std::is_trivial` for C++26. 378. [Chris Ever](https://github.com/chirsz-ever) added the `ignore_trailing_commas` parser option. 379. [Kuan-Fu Wu](https://github.com/kfwu1999) fixed the example code for `json_pointer` initialization. 380. [David Kilzer](https://github.com/ddkilzer) added a missing header to the input adapters. 381. [Miko](https://github.com/mikomikotaishi) added proper C++20 module support, simplified the module API, and fixed missing exports. 382. [hitgirl](https://github.com/hitgil) fixed the CMake configuration when cross-compiling. 383. [Devon Thomas](https://github.com/ThomaDevOSU) mentioned the Artistic Style formatting in the contribution guidelines. 384. [Erik Hu](https://github.com/Erikhu1) made Coveralls upload errors non-fatal in the CI. 385. [co63oc](https://github.com/co63oc) fixed typos. 386. [DmitriBogdanov](https://github.com/DmitriBogdanov) fixed broken package manager links in the documentation. 387. [Bander](https://github.com/banderzhm) improved the MSVC compatibility of the C++ modules. 388. [Andy Choi](https://github.com/ccpong) removed an unnecessary `template` keyword before `get` in the README and the documentation. 389. [SamareshSingh](https://github.com/ssam18) fixed single-element brace initialization to copy/move instead of wrapping in an array, fixed the `WITH_DEFAULT` macros for `ordered_map`, and handled moved events in `serve_header.py`. 390. [Aditya](https://github.com/Lumowhisp) improved the documentation of the documentation generation. 391. [cheese1](https://github.com/cheese1) clarified the README. 392. [KhloodElhossiny](https://github.com/khloodelhossiny) enabled `std::string_view` keys in `operator[]`. 393. [Charles Cabergs](https://github.com/cacharle) fixed a `-Wtautological-constant-out-of-range-compare` warning. 394. [EALePain](https://github.com/EALePain) made the `std::tuple` conversion work with reference types such as `std::tie`. 395. [koala_oishi](https://github.com/chibi-dogs) fixed grammatical wording in the README. 396. [riccardoori11](https://github.com/riccardoori11) fixed a typo in the documentation. 397. [Swastik Bose](https://github.com/VasuBhakt) fixed the parent pointers after `update()` with `JSON_DIAGNOSTICS` and fixed the Doxygen autolinking of requirements. 398. [trdesilva](https://github.com/trdesilva) added `front`, `pop_front`, and `push_front` to `json_pointer`. 399. [Akhilesh Arora](https://github.com/akhilesharora) fixed an incomplete-type error with `ordered_json`. 400. [Hariom Phulre](https://github.com/hariomphulre) fixed the C++20 modules compilation with GCC. 401. [Kirill Lokotkov](https://github.com/RUSLoker) fixed printing `long double` values. 402. [George Sedov](https://github.com/radistmorse) added the `NLOHMANN_DEFINE_TYPE_*_WITH_NAMES` macros. 403. [Caillin Nugent](https://github.com/nugentcaillin) added the `NLOHMANN_JSON_SERIALIZE_ENUM_STRICT` macro. 404. [Cosmin D.](https://github.com/drcosmin) fixed `std::filesystem::path` conversions and added an MSVC workaround for `std::unique_ptr`. 405. [Paul Dreik](https://github.com/pauldreik) fixed a test relying on implementation-specific behavior. 406. [Daniel Falk](https://github.com/daniel-falk) added missing copyright notices to the SBOM. 407. [Federico Sfriso](https://github.com/federicosfriso05-dotcom) added support for constructing JSON values from C++20 range views. 408. [Luke Banicevic](https://github.com/banaboi) fixed corrupt BSON output for lengths exceeding `INT32_MAX`, cleaned up the BSON writer, and improved the documentation. 409. [Patrick Armstrong](https://github.com/Patrick10199) updated the CBOR references and the half-precision float assertions. 410. [Yash Bavadiya](https://github.com/xevrion) added checks to all BSON reads. 411. [hum4nBeing](https://github.com/hum4nBeing) fixed the overflow handling of high-precision numbers in UBJSON. 412. [tomatotomata](https://github.com/tomatotomata) added checks for reading CBOR tagged subtypes. 413. [YingqiDuan](https://github.com/YingqiDuan) documented the BSON interoperability. 414. [KBS](https://github.com/youdie006) documented the standards compliance and the strictness of `parse()` and `operator>>`. 415. [Petr Bělohlávek](https://github.com/petrbel) added Clang 21 and 22 to the CI. 416. [Dmitry Rantovov](https://github.com/darkdi) fixed the placement of a CBOR documentation block. 417. [ljcjclljc](https://github.com/ljcjclljc) fixed the comparison of large unsigned integers with signed integers. 418. [Sahil Kamate](https://github.com/sahilkamate03) fixed the handling of CBOR tags 0-5 and 21-23. 419. [Krishnanand G](https://github.com/Krishnanand-G) made the UBJSON writer reject `use_type` without `use_size`. 420. [whn](https://github.com/Whning0513) documented the lenient BSON input handling and corrected the complexity of `to_bson`. 421. [elix3r](https://github.com/22elix3r) fixed `update()` with `merge_objects` when merging a primitive into an object. 422. [Avionic Harshit](https://github.com/avionicharshit-byte) made `diff()` linear when an array shrinks. 423. [Qatadaha Bin Matloob](https://github.com/qatcod) fixed comparisons between integers and floats and fixed unparsable BJData output. 424. [Wu Shuwen](https://github.com/dajiaohuang) removed an unused include. Thanks a lot for helping out! Please [let me know](mailto:mail@nlohmann.me) if I forgot someone. ## Used third-party tools The library itself consists of a single header file licensed under the MIT license. However, it is built, tested, documented, and whatnot using a lot of third-party tools and services. Thanks a lot! - [**amalgamate.py - Amalgamate C source and header files**](https://github.com/edlund/amalgamate) to create a single header file - [**American fuzzy lop**](https://lcamtuf.coredump.cx/afl/) for fuzz testing - [**AppVeyor**](https://www.appveyor.com) for [continuous integration](https://ci.appveyor.com/project/nlohmann/json) on Windows - [**Artistic Style**](https://astyle.sourceforge.net) for automatic source code indentation - [**Clang**](https://clang.llvm.org) for compilation with code sanitizers - [**Clang-Tidy**](https://clang.llvm.org/extra/clang-tidy/) for static analysis and style checks - [**CMake**](https://cmake.org) for build automation - [**Codacy**](https://www.codacy.com) for further [code analysis](https://app.codacy.com/gh/nlohmann/json/dashboard) - [**CodeQL**](https://codeql.github.com) for code scanning - [**Coveralls**](https://coveralls.io) to measure [code coverage](https://coveralls.io/github/nlohmann/json) - [**Coverity Scan**](https://scan.coverity.com) for [static analysis](https://scan.coverity.com/projects/nlohmann-json) - [**cppcheck**](https://cppcheck.sourceforge.io) for static analysis - [**cpplint**](https://github.com/cpplint/cpplint) for style checks - [**doctest**](https://github.com/doctest/doctest) for the unit tests - [**Flawfinder**](https://dwheeler.com/flawfinder/) for static analysis - [**GitHub Changelog Generator**](https://github.com/github-changelog-generator/github-changelog-generator) to generate the [ChangeLog](https://github.com/nlohmann/json/blob/develop/ChangeLog.md) - [**Google Benchmark**](https://github.com/google/benchmark) to implement the benchmarks - [**Hedley**](https://nemequ.github.io/hedley/) to avoid re-inventing several compiler-agnostic feature macros - [**include-what-you-use**](https://include-what-you-use.org) to check the included headers - [**Infer**](https://fbinfer.com) for static analysis - [**lcov**](https://github.com/linux-test-project/lcov) to process coverage information and create an HTML view - [**libFuzzer**](https://llvm.org/docs/LibFuzzer.html) to implement fuzz testing for OSS-Fuzz - [**Material for MkDocs**](https://squidfunk.github.io/mkdocs-material/) for the style of the documentation site - [**MkDocs**](https://www.mkdocs.org) for the documentation site - [**OSS-Fuzz**](https://github.com/google/oss-fuzz) for continuous fuzz testing of the library ([project repository](https://github.com/google/oss-fuzz/tree/master/projects/json)) - [**Probot**](https://probot.github.io) for automating maintainer tasks such as closing stale issues, requesting missing information, or detecting toxic comments. - [**Semgrep**](https://semgrep.dev) for static analysis - [**Valgrind**](https://valgrind.org) to check for correct memory management ## Notes ### Standards compliance The library targets strict conformance with [RFC 8259](https://tools.ietf.org/html/rfc8259.html). Both the original [JSONTestSuite](https://github.com/nst/JSONTestSuite) and its updated revision are exercised in CI; their test data is downloaded from [`nlohmann/json_test_data`](https://github.com/nlohmann/json_test_data) at configure time rather than committed to this repository (see [`tests/src/unit-testsuites.cpp`](https://github.com/nlohmann/json/blob/develop/tests/src/unit-testsuites.cpp)): - The updated revision runs all mandatory `y_` (must-accept) and `n_` (must-reject) cases through the strict [`parse()`](https://json.nlohmann.me/api/basic_json/parse/) entry point; the original suite runs its `n_` cases through `parse()` and its `y_` cases through [`operator>>`](https://json.nlohmann.me/api/operator_gtgt/). - The `i_` (implementation-defined) cases are, by RFC 8259, free to be accepted *or* rejected, so "passing all `i_` cases" is not a meaningful conformance metric. The library makes deliberate, documented choices there: nesting depth is not artificially limited, a leading UTF-8 byte order mark is silently ignored, [Unicode noncharacters](https://www.unicode.org/faq/private_use.html#nonchar1) are forwarded unchanged, invalid UTF-8 and lone/unpaired UTF-16 surrogates are rejected (stricter than required), and a number that cannot be stored without becoming `NaN`/`INF` raises [`out_of_range.406`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range406). One behavioral nuance is worth calling out, because a superficial test often misreads it as non-compliance: [`parse()`](https://json.nlohmann.me/api/basic_json/parse/) is strict and rejects trailing data after a value, whereas [`operator>>`](https://json.nlohmann.me/api/operator_gtgt/) follows relaxed iostream semantics — it parses a single value and leaves the stream positioned right after it. Feeding "a valid document followed by trailing bytes" through `operator>>` reports success; the same input through `parse()` is rejected. This is a documented two-API design, not a conformance gap. See [**parsing**](https://json.nlohmann.me/features/parsing/) for details. ### Character encoding The library supports **Unicode input** as follows: - Only **UTF-8** encoded input is supported, which is the default encoding for JSON according to [RFC 8259](https://tools.ietf.org/html/rfc8259.html#section-8.1). - `std::u16string` and `std::u32string` can be parsed, assuming UTF-16 and UTF-32 encoding, respectively. These encodings are not supported when reading from files or other input containers. - Other encodings such as Latin-1 or ISO 8859-1 are **not** supported and will yield parse or serialization errors. - [Unicode noncharacters](https://www.unicode.org/faq/private_use.html#nonchar1) will not be replaced by the library. - Invalid surrogates (e.g., incomplete pairs such as `\uDEAD`) will yield parse errors. - The strings stored in the library are UTF-8 encoded. When using the default string type (`std::string`), note that its length/size functions return the number of stored bytes rather than the number of characters or glyphs. - When you store strings with different encodings in the library, calling [`dump()`](https://json.nlohmann.me/api/basic_json/dump/) may throw an exception unless `json::error_handler_t::replace`, `json::error_handler_t::ignore`, or `json::error_handler_t::keep` are used as error handlers. - To store wide strings (e.g., `std::wstring`), you need to convert them to a UTF-8 encoded `std::string` before, see [an example](https://json.nlohmann.me/home/faq/#wide-string-handling). ### Comments in JSON This library does not support comments by default. It does so for three reasons: 1. Comments are not part of the [JSON specification](https://tools.ietf.org/html/rfc8259). You may argue that `//` or `/* */` are allowed in JavaScript, but JSON is not JavaScript. 2. This was not an oversight: Douglas Crockford [wrote on this](https://news.ycombinator.com/item?id=3912149) in May 2012: > I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have destroyed interoperability. I know that the lack of comments makes some people sad, but it shouldn't. > > Suppose you are using JSON to keep configuration files, which you would like to annotate. Go ahead and insert all the comments you like. Then pipe it through JSMin before handing it to your JSON parser. 3. It is dangerous for interoperability if some libraries would add comment support while others don't. Please check [The Harmful Consequences of the Robustness Principle](https://tools.ietf.org/html/draft-iab-protocol-maintenance-01) on this. However, you can set parameter `ignore_comments` to true in the `parse` function to ignore `//` or `/* */` comments. Comments will then be treated as whitespace. ### Trailing commas The JSON specification does not allow trailing commas in arrays and objects, and hence this library is treating them as parsing errors by default. Like comments, you can set parameter `ignore_trailing_commas` to true in the `parse` function to ignore trailing commas in arrays and objects. Note that a single comma as the only content of the array or object (`[,]` or `{,}`) is not allowed, and multiple trailing commas (`[1,,]`) are not allowed either. This library does not add trailing commas when serializing JSON data. For more information, see [JSON With Commas and Comments (JWCC)](https://nigeltao.github.io/blog/2021/json-with-commas-comments.html). ### Order of object keys By default, the library does not preserve the **insertion order of object elements**. This is standards-compliant, as the [JSON standard](https://tools.ietf.org/html/rfc8259.html) defines objects as "an unordered collection of zero or more name/value pairs". If you do want to preserve the insertion order, you can try the type [`nlohmann::ordered_json`](https://github.com/nlohmann/json/issues/2179). Alternatively, you can use a more sophisticated ordered map like [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) ([integration](https://github.com/nlohmann/json/issues/546#issuecomment-304447518)) or [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map) ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)). See the [**documentation on object order**](https://json.nlohmann.me/features/object_order/) for more information. ### Memory Release We checked with Valgrind and the Address Sanitizer (ASAN) that there are no memory leaks. If you find that a parsing program with this library does not release memory, please consider the following case, and it may be unrelated to this library. **Your program is compiled with glibc.** There is a tunable threshold that glibc uses to decide whether to actually return memory to the system or whether to cache it for later reuse. If in your program you make lots of small allocations and those small allocations are not a contiguous block and are presumably below the threshold, then they will not get returned to the OS. Here is a related issue [#1924](https://github.com/nlohmann/json/issues/1924). ### Further notes - The code contains numerous debug **assertions** which can be switched off by defining the preprocessor macro `NDEBUG`, see the [documentation of `assert`](https://en.cppreference.com/w/cpp/error/assert). In particular, note [`operator[]`](https://json.nlohmann.me/api/basic_json/operator%5B%5D/) implements **unchecked access** for const objects: If the given key is not present, the behavior is undefined (think of a dereferenced null pointer) and yields an [assertion failure](https://github.com/nlohmann/json/issues/289) if assertions are switched on. If you are not sure whether an element in an object exists, use checked access with the [`at()` function](https://json.nlohmann.me/api/basic_json/at/). Furthermore, you can define `JSON_ASSERT(x)` to replace calls to `assert(x)`. See the [**documentation on runtime assertions**](https://json.nlohmann.me/features/assertions/) for more information. - As the exact number type is not defined in the [JSON specification](https://tools.ietf.org/html/rfc8259.html), this library tries to choose the best fitting C++ number type automatically. As a result, the type `double` may be used to store numbers which may yield [**floating-point exceptions**](https://github.com/nlohmann/json/issues/181) in certain rare situations if floating-point exceptions have been unmasked in the calling code. These exceptions are not caused by the library and need to be fixed in the calling code, such as by re-masking the exceptions prior to calling library functions. - The code can be compiled without C++ **runtime type identification** features; that is, you can use the `-fno-rtti` compiler flag. - **Exceptions** are used widely within the library. They can, however, be switched off with either using the compiler flag `-fno-exceptions` or by defining the symbol `JSON_NOEXCEPTION`. In this case, exceptions are replaced by `abort()` calls. You can further control this behavior by defining `JSON_THROW_USER` (overriding `throw`), `JSON_TRY_USER` (overriding `try`), and `JSON_CATCH_USER` (overriding `catch`). Note that `JSON_THROW_USER` should leave the current scope (e.g., by throwing or aborting), as continuing after it may yield undefined behavior. Note the explanatory [`what()`](https://en.cppreference.com/w/cpp/error/exception/what) string of exceptions is not available for MSVC if exceptions are disabled, see [#2824](https://github.com/nlohmann/json/discussions/2824). See the [**documentation of exceptions**](https://json.nlohmann.me/home/exceptions/) for more information. ## Execute unit tests To compile and run the tests, you need to execute ```shell mkdir build cd build cmake .. -DJSON_BuildTests=On cmake --build . ctest --output-on-failure ``` Note that during the `ctest` stage, several JSON test files are downloaded from an [external repository](https://github.com/nlohmann/json_test_data). If policies forbid downloading artifacts during testing, you can download the files yourself and pass the directory with the test files via `-DJSON_TestDataDirectory=path` to CMake. Then, no Internet connectivity is required. See [issue #2189](https://github.com/nlohmann/json/issues/2189) for more information. If the testdata is not found, several test suites will fail like this: ``` =============================================================================== json/tests/src/make_test_data_available.hpp:26: TEST CASE: check test suite is downloaded json/tests/src/make_test_data_available.hpp:28: FATAL ERROR: REQUIRE( utils::check_testsuite_downloaded() ) is NOT correct! values: REQUIRE( false ) logged: Test data not found in 'json/cmake-build-debug/json_test_data'. Please execute target 'download_test_data' before running this test suite. See <https://github.com/nlohmann/json#execute-unit-tests> for more information. =============================================================================== ``` In case you have downloaded the library rather than checked out the code via Git, test `cmake_fetch_content_configure` will fail. Please execute `ctest -LE git_required` to skip these tests. See [issue #2189](https://github.com/nlohmann/json/issues/2189) for more information. Some tests require network access to execute properly. They are labeled as `git_required`. Please execute `ctest -LE git_required` to skip these tests. See [issue #4851](https://github.com/nlohmann/json/issues/4851) for more information. Some tests change the installed files and hence make the whole process not reproducible. Please execute `ctest -LE not_reproducible` to skip these tests. See [issue #2324](https://github.com/nlohmann/json/issues/2324) for more information. Furthermore, assertions must be switched off to ensure reproducible builds (see [discussion 4494](https://github.com/nlohmann/json/discussions/4494)). Note you need to call `ctest -LE "not_reproducible|git_required"` to exclude both labels. See [issue #2596](https://github.com/nlohmann/json/issues/2596) for more information. As Intel compilers use unsafe floating point optimization by default, the unit tests may fail. Use flag [`/fp:precise`](https://www.intel.com/content/www/us/en/docs/cpp-compiler/developer-guide-reference/2021-8/fp-model-fp.html) then.
Live Chat
