README.md

• Design goals
• Sponsors
• Integration
  • CMake
  • Package Managers
  • Pkg-config
• Examples
  • JSON as first-class data type
  • Serialization / Deserialization
  • STL-like access
  • Conversion from STL containers
  • JSON Pointer and JSON Patch
  • JSON Merge Patch
  • Implicit conversions
  • Conversions to/from arbitrary types
  • Specializing enum conversion
  • Binary formats (BSON, CBOR, MessagePack, and UBJSON)
• Supported compilers
• License
• Contact
• Thanks
• Used third-party tools
• Projects using JSON for Modern C++
• Notes
• Execute unit tests

Design goals

There are myriads of JSON 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 and you'll know what I mean.

• Trivial integration. Our whole code consists of a single header file 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 class is heavily unit-tested and covers 100% of the code, including all exceptional behavior. Furthermore, we checked with Valgrind and the Clang Sanitizers that there are no memory leaks. Google OSS-Fuzz 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.

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 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 for more information.

Sponsors

You can sponsor this library at GitHub Sponsors.

🏷 Named Sponsors

• Michael Hartmann
• Stefan Hagen
• Steve Sperandeo

Thanks everyone!

Integration

json.hpp is the single required file in single_include/nlohmann or released here. You need to add

#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 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