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- [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))
- [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 first-class data type](#json-as-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, and BJData)](#binary-formats-bson-cbor-messagepack-ubjson-and-bjdata)
- [Supported compilers](#supported-compilers)
- [Integration](#integration)
- [CMake](#cmake)
- [Package Managers](#package-managers)
- [Pkg-config](#pkg-config)
- [License](#license)
- [Contact](#contact)
- [Thanks](#thanks)
- [Used third-party tools](#used-third-party-tools)
- [Projects using JSON for Modern C++](#projects-using-json-for-modern-c)
- [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.
- **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 [Core Infrastructure Initiative (CII) best practices](https://bestpractices.coreinfrastructure.org/projects/289).
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/master/.github/CONTRIBUTING.md#please-dont) for more information.
## Sponsors
You can sponsor this library at [GitHub Sponsors](https://github.com/sponsors/nlohmann).
### :office: Corporate Sponsor
[](https://github.com/codacy)
### :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)
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/
【C++ JSON 开源库】nlohmann 可直接使用的源码
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更新于2023-11-15
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JSON（JavaScript Object Notation）是一种轻量级的数据交换格式，被广泛用于Web服务和应用程序之间的数据传输。在C++编程中，处理JSON数据通常需要借助第三方库，nlohmann就是一个非常流行的C++ JSON解析和生成库。这个开源库由Niels Lohmann编写，它以其高效、易于使用和丰富的功能而受到开发者们的喜爱。
nlohmann/json库的使用非常简单，正如描述中提到的，你只需要将下载的`json-master`文件夹放入你的项目代码目录中，然后在需要使用JSON的地方包含头文件`#include "./json-master/include/nlohmann/json.hpp"`。这样，你就可以直接利用nlohmann/json库来解析和生成JSON对象。
在C++中，nlohmann/json库提供了一种类型安全的方式来操作JSON数据。它可以将C++的内置类型、自定义类、STL容器等直接转换为JSON对象，反之亦然。例如，你可以直接将一个C++的std::vector或std::map转换为JSON数组或对象，而无需手动构建JSON字符串。
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
// 创建一个JSON对象
json j;
j["name"] = "John";
j["age"] = 30;
j["city"] = "New York";
// 将JSON对象转换为字符串
std::string jsonString = j.dump();
// 解析JSON字符串
json j2 = json::parse(jsonString);
// 从JSON对象中获取数据
std::string name = j2["name"];
int age = j2["age"];
```
nlohmann/json库还支持流式API，允许你在一行代码中构建复杂的JSON结构，这在处理大量JSON数据时非常有用。此外，它提供了错误处理机制，当解析JSON时遇到问题，库会抛出异常，帮助开发者定位问题。
```cpp
try {
json j = R"({"key": "value", "array": [1, 2, 3]})"_json;
} catch (const std::exception& e) {
std::cerr << "Error: " << e.what() << '\n';
}
```
对于更复杂的数据类型，如自定义类，你需要实现`to_json()`和`from_json()`方法，使它们能够与nlohmann/json库进行序列化和反序列化操作。
```cpp
struct Person {
std::string name;
int age;
void to_json(json& j) const {
j = {{"name", name}, {"age", age}};
}
void from_json(const json& j) {
j.at("name").get_to(name);
j.at("age").get_to(age);
}
};
```
nlohmann/json库是C++开发中处理JSON数据的强大工具。它的易用性、灵活性和高性能使得它在各种项目中都得到了广泛应用。通过简单地将其源代码引入项目并包含对应的头文件，你就能享受到它带来的便利。
【C++ JSON 开源库】nlohmann 可直接使用的源码 （1072个子文件） 
meson.build 629B StandaloneFuzzTargetMain.c 2KB CITATION.cff 410B lit.cfg 1KB lit.cfg 214B .clang-format 2KB .clang-tidy 2KB ci.cmake 44KB test.cmake 10KB download_test_data.cmake 3KB CODEOWNERS 271B unit-bjdata.cpp 175KB unit-cbor.cpp 126KB unit-ubjson.cpp 110KB unit-testsuites.cpp 102KB unit-element_access2.cpp 94KB unit-msgpack.cpp 85KB unit-class_parser.cpp 83KB unit-iterators2.cpp 54KB unit-regression1.cpp 53KB unit-conversions.cpp 53KB unit-constructor1.cpp 52KB unit-iterators1.cpp 49KB unit-json_patch.cpp 46KB unit-deserialization.cpp 44KB unit-bson.cpp 43KB unit-element_access1.cpp 39KB unit-items.cpp 35KB unit-to_chars.cpp 34KB unit-modifiers.cpp 32KB unit-comparison.cpp 30KB unit-json_pointer.cpp 30KB unit-regression2.cpp 28KB FuzzerUnittest.cpp 28KB unit-unicode1.cpp 26KB FuzzerLoop.cpp 25KB unit-udt.cpp 22KB unit-pointer_access.cpp 21KB unit-unicode2.cpp 20KB FuzzerMutate.cpp 19KB FuzzerDriver.cpp 18KB unit-class_iterator.cpp 16KB unit-capacity.cpp 16KB unit-reference_access.cpp 14KB unit-class_const_iterator.cpp 14KB unit-inspection.cpp 14KB FuzzerTracePC.cpp 12KB unit-serialization.cpp 11KB FuzzerTraceState.cpp 11KB afl_driver.cpp 11KB unit-udt_macro.cpp 11KB unit-class_lexer.cpp 11KB unit-unicode4.cpp 11KB unit-unicode5.cpp 11KB unit-unicode3.cpp 11KB unit-binary_formats.cpp 10KB unit-readme.cpp 10KB unit-algorithms.cpp 10KB unit-ordered_map.cpp 9KB FuzzerMerge.cpp 9KB unit-diagnostics.cpp 8KB benchmarks.cpp 8KB unit-alt-string.cpp 8KB FuzzerIOWindows.cpp 8KB unit-merge_patch.cpp 7KB unit-allocator.cpp 7KB basic_json__CompatibleType.cpp 6KB FuzzerUtil.cpp 6KB unit-convenience.cpp 6KB FuzzerUtilDarwin.cpp 5KB FuzzerSHA1.cpp 5KB unit-concepts.cpp 5KB FuzzerUtilWindows.cpp 5KB unit-32bit.cpp 5KB unit-constructor2.cpp 5KB unit-hash.cpp 4KB unit-noexcept.cpp 3KB sax_parse.cpp 3KB unit-user_defined_input.cpp 3KB FuzzerIO.cpp 3KB FuzzerUtilPosix.cpp 3KB sax_parse__binary.cpp 3KB unit-byte_container_with_subtype.cpp 3KB fuzzer-parse_bjdata.cpp 3KB fuzzer-parse_ubjson.cpp 3KB at__json_pointer.cpp 2KB unit-wstring.cpp 2KB unit-ordered_json.cpp 2KB CallerCalleeTest.cpp 2KB FuzzerIOPosix.cpp 2KB unit-type_traits.cpp 2KB at__json_pointer_const.cpp 2KB fuzzer-parse_bson.cpp 2KB unit-udl.cpp 2KB fuzzer-parse_msgpack.cpp 2KB FuzzerCrossOver.cpp 2KB unit-disabled_exceptions.cpp 2KB fuzzer-parse_cbor.cpp 2KB FuzzerExtFunctionsWeakAlias.cpp 2KB fuzzer-parse_json.cpp 2KB共 1072 条
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