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A fast JSON parser/generator for C++ with both SAX/DOM style API

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Quick Overview

RapidJSON is a fast JSON parser/generator for C++ with both SAX/DOM style APIs. It aims to be the fastest JSON parser and generator, with a lightweight and easy-to-use API. RapidJSON is widely used in various C++ projects that require JSON processing.

Pros

  • Extremely fast performance for both parsing and generation
  • Low memory footprint
  • Easy to integrate with existing C++ projects
  • Supports both DOM and SAX parsing styles

Cons

  • Lacks some advanced features found in other JSON libraries
  • Documentation can be sparse in some areas
  • May require careful handling to avoid security vulnerabilities
  • Limited support for non-standard JSON extensions

Code Examples

  1. Parsing a JSON string:
#include "rapidjson/document.h"

const char* json = "{\"project\":\"rapidjson\",\"stars\":10000}";
rapidjson::Document d;
d.Parse(json);

assert(d["project"].IsString());
printf("Project: %s\n", d["project"].GetString());
  1. Generating JSON:
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"

rapidjson::StringBuffer buffer;
rapidjson::Writer<rapidjson::StringBuffer> writer(buffer);

writer.StartObject();
writer.Key("name");
writer.String("RapidJSON");
writer.Key("version");
writer.Int(1);
writer.EndObject();

std::cout << buffer.GetString() << std::endl;
  1. Modifying a JSON document:
#include "rapidjson/document.h"

rapidjson::Document d;
d.SetObject();

rapidjson::Value array(rapidjson::kArrayType);
array.PushBack(1, d.GetAllocator()).PushBack(2, d.GetAllocator());

d.AddMember("array", array, d.GetAllocator());
d["array"].PushBack(3, d.GetAllocator());

Getting Started

  1. Clone the RapidJSON repository:

    git clone https://github.com/Tencent/rapidjson.git

  2. Include RapidJSON headers in your project:

    #include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"

  3. Compile your project with C++11 support:

    g++ -std=c++11 your_file.cpp -I/path/to/rapidjson/include

  4. Start using RapidJSON in your C++ code as shown in the examples above.

Competitor Comparisons

miloyip logo

nativejson-benchmark

1,973

C/C++ JSON parser/generator benchmark

Pros of nativejson-benchmark

  • Focuses specifically on benchmarking JSON parsing performance
  • Provides comprehensive comparisons across multiple JSON libraries
  • Offers detailed performance metrics and visualizations

Cons of nativejson-benchmark

  • Limited to benchmarking functionality, not a full-featured JSON library
  • May not be as actively maintained as rapidjson
  • Smaller community and ecosystem compared to rapidjson

Code Comparison

nativejson-benchmark (benchmark code):

void parse_rapidjson(Benchmark& benchmark, const char* json, size_t length) {
    rapidjson::Document d;
    benchmark.run([&]() {
        d.Parse(json, length);
    });
}

rapidjson (parsing code):

rapidjson::Document d;
d.Parse(json);
if (d.HasParseError()) {
    // Handle parsing error
}

Summary

nativejson-benchmark is a specialized tool for benchmarking JSON parsing performance across various libraries, including rapidjson. It offers detailed comparisons and visualizations but is limited to benchmarking functionality. rapidjson, on the other hand, is a full-featured JSON library with a larger community and more active development. While nativejson-benchmark is excellent for performance testing, rapidjson is better suited for general JSON parsing and manipulation in production environments.

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Pros of nlohmann/json

  • Easier to use with a more intuitive API
  • Header-only library, simplifying integration
  • Extensive documentation and examples

Cons of nlohmann/json

  • Slower parsing and serialization compared to rapidjson
  • Higher memory usage for large JSON documents

Code Comparison

nlohmann/json:

#include <nlohmann/json.hpp>
using json = nlohmann::json;

json j = {
  {"name", "John"},
  {"age", 30},
  {"city", "New York"}
};
std::string s = j.dump();

rapidjson:

#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
using namespace rapidjson;

Document d;
d.SetObject();
d.AddMember("name", "John", d.GetAllocator());
d.AddMember("age", 30, d.GetAllocator());
d.AddMember("city", "New York", d.GetAllocator());
StringBuffer buffer;
Writer<StringBuffer> writer(buffer);
d.Accept(writer);
std::string s = buffer.GetString();

The code comparison demonstrates that nlohmann/json offers a more concise and intuitive syntax for creating and manipulating JSON objects, while rapidjson requires more verbose code and explicit memory management.

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simdjson

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Parsing gigabytes of JSON per second : used by Facebook/Meta Velox, the Node.js runtime, ClickHouse, WatermelonDB, Apache Doris, Milvus, StarRocks

Pros of simdjson

  • Significantly faster parsing and validation of JSON documents, especially for large files
  • Lower memory usage due to its efficient parsing technique
  • Designed with modern CPU architectures in mind, utilizing SIMD instructions

Cons of simdjson

  • Limited to parsing and validating JSON; doesn't offer serialization capabilities
  • Requires C++17 or newer, which may not be available in all environments
  • Less mature and less widely adopted compared to RapidJSON

Code Comparison

RapidJSON:

Document d;
d.Parse(json);
if (d.HasParseError()) {
    // Handle error
}

simdjson:

ondemand::parser parser;
auto json = padded_string::load("file.json");
ondemand::document doc = parser.iterate(json);

Both libraries offer efficient JSON parsing, but simdjson focuses on high-speed parsing and validation using modern CPU features, while RapidJSON provides a more comprehensive JSON manipulation toolkit. simdjson excels in performance-critical scenarios with large JSON datasets, whereas RapidJSON offers broader functionality and wider compatibility across different C++ versions and platforms.

open-source-parsers logo

jsoncpp

8,063

A C++ library for interacting with JSON.

Pros of jsoncpp

  • Easier to use and integrate, with a simpler API
  • Better support for older compilers and platforms
  • More mature and stable, with a longer development history

Cons of jsoncpp

  • Slower parsing and serialization performance
  • Larger memory footprint
  • Less actively maintained compared to rapidjson

Code Comparison

jsoncpp:

Json::Value root;
Json::Reader reader;
bool parsingSuccessful = reader.parse(jsonString, root);
if (parsingSuccessful) {
    std::string name = root["name"].asString();
}

rapidjson:

rapidjson::Document document;
document.Parse(jsonString.c_str());
if (!document.HasParseError()) {
    std::string name = document["name"].GetString();
}

Both libraries offer JSON parsing and manipulation capabilities, but rapidjson focuses on performance and low memory usage, while jsoncpp prioritizes ease of use and broader compatibility. The choice between them depends on specific project requirements, such as performance needs, target platforms, and developer preferences.

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README

RapidJSON logo

Release version

A fast JSON parser/generator for C++ with both SAX/DOM style API

Tencent is pleased to support the open source community by making RapidJSON available.

Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip.

Build status

LinuxWindowsCoveralls
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Introduction

RapidJSON is a JSON parser and generator for C++. It was inspired by RapidXml.

  • RapidJSON is small but complete. It supports both SAX and DOM style API. The SAX parser is only a half thousand lines of code.

  • RapidJSON is fast. Its performance can be comparable to strlen(). It also optionally supports SSE2/SSE4.2 for acceleration.

  • RapidJSON is self-contained and header-only. It does not depend on external libraries such as BOOST. It even does not depend on STL.

  • RapidJSON is memory-friendly. Each JSON value occupies exactly 16 bytes for most 32/64-bit machines (excluding text string). By default it uses a fast memory allocator, and the parser allocates memory compactly during parsing.

  • RapidJSON is Unicode-friendly. It supports UTF-8, UTF-16, UTF-32 (LE & BE), and their detection, validation and transcoding internally. For example, you can read a UTF-8 file and let RapidJSON transcode the JSON strings into UTF-16 in the DOM. It also supports surrogates and "\u0000" (null character).

More features can be read here.

JSON(JavaScript Object Notation) is a light-weight data exchange format. RapidJSON should be in full compliance with RFC7159/ECMA-404, with optional support of relaxed syntax. More information about JSON can be obtained at

Highlights in v1.1 (2016-8-25)

For other changes please refer to change log.

Compatibility

RapidJSON is cross-platform. Some platform/compiler combinations which have been tested are shown as follows.

  • Visual C++ 2008/2010/2013 on Windows (32/64-bit)
  • GNU C++ 3.8.x on Cygwin
  • Clang 3.4 on Mac OS X (32/64-bit) and iOS
  • Clang 3.4 on Android NDK

Users can build and run the unit tests on their platform/compiler.

Installation

RapidJSON is a header-only C++ library. Just copy the include/rapidjson folder to system or project's include path.

Alternatively, if you are using the vcpkg dependency manager you can download and install rapidjson with CMake integration in a single command:

  • vcpkg install rapidjson

RapidJSON uses following software as its dependencies:

  • CMake as a general build tool
  • (optional) Doxygen to build documentation
  • (optional) googletest for unit and performance testing

To generate user documentation and run tests please proceed with the steps below:

  1. Execute git submodule update --init to get the files of thirdparty submodules (google test).
  2. Create directory called build in rapidjson source directory.
  3. Change to build directory and run cmake .. command to configure your build. Windows users can do the same with cmake-gui application.
  4. On Windows, build the solution found in the build directory. On Linux, run make from the build directory.

On successful build you will find compiled test and example binaries in bin directory. The generated documentation will be available in doc/html directory of the build tree. To run tests after finished build please run make test or ctest from your build tree. You can get detailed output using ctest -V command.

It is possible to install library system-wide by running make install command from the build tree with administrative privileges. This will install all files according to system preferences. Once RapidJSON is installed, it is possible to use it from other CMake projects by adding find_package(RapidJSON) line to your CMakeLists.txt.

Usage at a glance

This simple example parses a JSON string into a document (DOM), make a simple modification of the DOM, and finally stringify the DOM to a JSON string.

// rapidjson/example/simpledom/simpledom.cpp`
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
#include <iostream>

using namespace rapidjson;

int main() {
    // 1. Parse a JSON string into DOM.
    const char* json = "{\"project\":\"rapidjson\",\"stars\":10}";
    Document d;
    d.Parse(json);

    // 2. Modify it by DOM.
    Value& s = d["stars"];
    s.SetInt(s.GetInt() + 1);

    // 3. Stringify the DOM
    StringBuffer buffer;
    Writer<StringBuffer> writer(buffer);
    d.Accept(writer);

    // Output {"project":"rapidjson","stars":11}
    std::cout << buffer.GetString() << std::endl;
    return 0;
}

Note that this example did not handle potential errors.

The following diagram shows the process.

simpledom

More examples are available:

  • DOM API

  • SAX API

    • simplereader: Dumps all SAX events while parsing a JSON by Reader.
    • condense: A command line tool to rewrite a JSON, with all whitespaces removed.
    • pretty: A command line tool to rewrite a JSON with indents and newlines by PrettyWriter.
    • capitalize: A command line tool to capitalize strings in JSON.
    • messagereader: Parse a JSON message with SAX API.
    • serialize: Serialize a C++ object into JSON with SAX API.
    • jsonx: Implements a JsonxWriter which stringify SAX events into JSONx (a kind of XML) format. The example is a command line tool which converts input JSON into JSONx format.

  • Schema

    • schemavalidator : A command line tool to validate a JSON with a JSON schema.

  • Advanced

    • prettyauto: A modified version of pretty to automatically handle JSON with any UTF encodings.
    • parsebyparts: Implements an AsyncDocumentParser which can parse JSON in parts, using C++11 thread.
    • filterkey: A command line tool to remove all values with user-specified key.
    • filterkeydom: Same tool as above, but it demonstrates how to use a generator to populate a Document.

Contributing

RapidJSON welcomes contributions. When contributing, please follow the code below.

Issues

Feel free to submit issues and enhancement requests.

Please help us by providing minimal reproducible examples, because source code is easier to let other people understand what happens. For crash problems on certain platforms, please bring stack dump content with the detail of the OS, compiler, etc.

Please try breakpoint debugging first, tell us what you found, see if we can start exploring based on more information been prepared.

Workflow

In general, we follow the "fork-and-pull" Git workflow.

  1. Fork the repo on GitHub
  2. Clone the project to your own machine
  3. Checkout a new branch on your fork, start developing on the branch
  4. Test the change before commit, Make sure the changes pass all the tests, including unittest and preftest, please add test case for each new feature or bug-fix if needed.
  5. Commit changes to your own branch
  6. Push your work back up to your fork
  7. Submit a Pull request so that we can review your changes

NOTE: Be sure to merge the latest from "upstream" before making a pull request!

Copyright and Licensing

You can copy and paste the license summary from below.

Tencent is pleased to support the open source community by making RapidJSON available.

Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip.

Licensed under the MIT License (the "License"); you may not use this file except
in compliance with the License. You may obtain a copy of the License at

http://opensource.org/licenses/MIT

Unless required by applicable law or agreed to in writing, software distributed 
under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
CONDITIONS OF ANY KIND, either express or implied. See the License for the 
specific language governing permissions and limitations under the License.