JSON++ v1.15 A set of C++ classes to support JSON / JSON5

I have been working with JSON recently in a number of C++ projects and wanted to learn it by understanding the JSON specification by writing my own JSON parser / encoder. There are a number of nice JSON libraries for C++ out there such as SimpleJSON and JSON for Modern C++. I particularly liked the SimpleJSON library which was able to implement a nice JSON parser / encoder in c. 1500 lines of code. I decided to write my own class based on SimpleJSON but using some modern C++ features such as r-value references, move constructors and operator=. Thus was born JSON++. Included in the download is the JSON++ source code and a VC 2017 application to fully exercise all the functionality of JSON++. The main class provided is CValue and is implemented in a JSONPP namespace. All the constructors of the CValue class allow a JSON value object to be constructed directly from other C++ types such as bool, double, long, STL strings, STL vectors, STL maps etc. Standard C++ operator= methods are also provided which mirror the constructor methods. The class also supports construction and assignment from C++ r-value references. A "Parse" method of CValue allows a JSON encoded string (either UTF8 or UTF16) to be parsed into the CValue instance. An "Encode" method allows a JSON encoded string in the form of a std::wstring to be created from a CValue instance. Various other CValue methods are modeled on the SimpleJSON classes.

Features

• Provides a complete JSON and JSON5 parser and encoder in c. 2300 lines of C++.
• All the code is provided in a single C++ Header only module of "JSON++.h" .
• All the code clean compiles at warning level 4, is /analyze and /permissive- clean and includes ASCII, Unicode, x86 and x64 built configurations.
• The class supports both UTF8 and UTF16 encoded JSON.
• Performance testing of the code has shown that JSON++ is about 50% faster than SimpleJSON for parsing. This is mainly achieved through the use of r-value references and placement new to avoid use of explicit heap memory allocations which SimpleJSON is forced to use. The encoding speed of JSON++ is the same as SimpleJSON, although support is provided in JSON++ for pretty printing the resulting JSON.
• Performance testing for parsing of a c. 400 character UTF16 JSON string on my Core I7 quad core 4Ghz development machine indicates a performance of about 30 MB / second.
• Encoding performance works out at about 100,000 encodes per second for a c. 400 character JSON string on my Core I7 machine.
• If a parsing error occurs during a call to the CValue::Parse method, then a JSONPP::CParseException will be thrown. This class provides a "m_Reason" enum value which specifies why the parsing failed and a "m_nIndex" value which specifies where the parsing error occurred in the JSON encoded text.
• The classes are only supported on VC 2017 or later.
• Provides support for JSON pointer (https://tools.ietf.org/html/rfc6901) via a simple JSONPP::CValue::JSONPointer method.
• Provides support for JSON5 (https://spec.json5.org/) parsing and encoding in addition to JSON.

The enclosed zip file contains the JSON++ source code and a VC 2017 console based application which exercises all of the JSON++ functionality.

Copyright

• You are allowed to include the source code in any product (commercial, shareware, freeware or otherwise) when your product is released in binary form.
• You are allowed to modify the source code in any way you want except you cannot modify the copyright details at the top of each module.
• If you want to distribute source code with your application, then you are only allowed to distribute versions released by the author. This is to maintain a single distribution point for the source code.

Usage

• To use the JSON++ classes in your project simply #include "JSON++.h" in which ever of the modules in your application requires the JSON functionality. The header file will look after pulling in any dependent header files
• As the code internally uses std::variant, your project will need to specify the /std:c++17 compiler setting or later.
• That should be it. You should now have a fully functional JSON parser and encoder now available to your Windows C++ application.

Updates

v1.15 (9 July 2023)

• Updated the class to provide support for JSON5 (https://spec.json5.org/) parsing and encoding.The JSON5 implementation in JSON++ follows the guidelines which SQLite3 used (https://www.sqlite.org/json1.html#json5) when it was updated to support JSON5. To support parsing of JSON5, you can pass the JSONPP::PARSE_FLAGS::PARSE_JSON5 value as the third parameter to the CValue::Parse method. If you pass a zero instead for this parameter then the method will revert to strict JSON parsing. To support JSON5 encoding you can pass the JSONPP::ENCODE_FLAGS::ENCODE_JSON5 value as the first parameter to the CValue::Encode method. Please see the example code in main.cpp for further examples.

v1.14 (12 May 2023)

• Updated copyright details
• Updated module to indicate that it needs to be compiled using /std:c++17. Thanks to Martin Richter for reporting this issue.

v1.13 (22 April 2022)

• Fixed a bug in CValue::operator=(const wchar_t*) where the m_Data member variable would get initialized incorrectly to a bool on VS 2022. Thanks to "jls" for reporting this issue.

v1.12 (29 January 2022)

• Updated copyright details.
• Fixed more static code analysis warnings in Visual Studio 2022.
• Updated the code to use C++ uniform initialization for all variable declarations.

v1.11 (2 November 2021)

• Updated copyright details.
• Updated compiler settings to more modern defaults.

v1.10 (23 May 2020)

• Added const versions of the CValue::Child methods.
• Added [[nodiscard]] to a number of CValue methods.

v1.09 (29 January 2020)

• Updated copyright details.
• Fixed more Clang-Tidy static code analysis warnings in the code.

v1.08 (16 December 2019)

• Fixed various Clang-Tidy static code analysis warnings in the code.

v1.07 (3 August 2019)

• Added comprehensive SAL annotations to all the code.

v1.06 (22 April 2019)

• Updated copyright details.
• Updated the code to clean compile on VC 2019.

v1.05 (2 September 2018)

• Fixed a number of compiler warnings when using VS 2017 15.8.2.

v1.04 (31 July 2018)

• Reworked code to use Windows API calls MultiByteToWideChar API for the UTF8 to UTF16 conversion rather than the deprecated codecvt header.

v1.03 (30 June 2018)

• Reworked the implementation to use std::variant. This does mean that the code now requires at least the /std:c++17 compiler setting. This has resulted in the module shrinking by c. 160 lines. Testing shows the performance remains the same as before.

v1.02 (29 May 2018)

• Fixed a number of C++ core guidelines compiler warnings.

v1.01 (10 January 2018)

• Updated copyright details.
• Added support for JSON Pointer (https://tools.ietf.org/html/rfc6901) support to the code via a new CValue::JSONPointer method.
• Made a number of methods of the CValue class static as they did not need to be non-static.

V1.0 (25 November 2017)

• Initial public release.