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Introduction

JSON (JavaScript Object Notation) is a lightweight data-interchange format. It can represent integer, real number, string, an ordered sequence of value, and a collection of name/value pairs.

Here is an example of JSON data:

{
    "encoding" : "UTF-8",
    "plug-ins" : [
        "python",
        "c++",
        "ruby"
        ],
    "indent" : { "length" : 3, "use_space": true }
}

And here it is with comments:

// Configuration options
{
    // Default encoding for text
    "encoding" : "UTF-8",
    
    // Plug-ins loaded at start-up
    "plug-ins" : [
        "python",
        "c++",
        "ruby"
        ],
        
    // Tab indent size
    "indent" : { "length" : 3, "use_space": true }
}

Features of jsoncpp

• Read and write JSON document.
• Attach C and C++ style comments to element during parsing.
• Rewrite JSON document preserving original comments.

Code example

#include <json/value.h>

Json::Value root;   // starts as "null"; will contain the root value after parsing
std::cin >> root;

// Get the value of the member of root named 'encoding', return 'UTF-8' if there is no
// such member.
std::string encoding = root.get("encoding", "UTF-8" ).asString();
// Get the value of the member of root named 'plug-ins', return a 'null' value if
// there is no such member.
const Json::Value plugins = root["plug-ins"];
for ( int index = 0; index < plugins.size(); ++index )  // Iterates over the sequence elements.
   loadPlugIn( plugins[index].asString() );
   
setIndentLength( root["indent"].get("length", 3).asInt() );
setIndentUseSpace( root["indent"].get("use_space", true).asBool() );

// ...
// At application shutdown to make the new configuration document:
// Since Json::Value has implicit constructor for all value types, it is not
// necessary to explicitly construct the Json::Value object:
root["encoding"] = getCurrentEncoding();
root["indent"]["length"] = getCurrentIndentLength();
root["indent"]["use_space"] = getCurrentIndentUseSpace();

// Make a new JSON document with the new configuration. Preserve original comments.
std::cout << root << "\n";

You can also read from a file, e.g.:

#include <fstream>

std::ifstream config_doc("config_doc.json", std::ifstream::binary);

If you need some unusual features, use Builders:

Json::Value root;
Json::CharReaderBuilder rbuilder;
// Configure the Builder, then ...
std::string errs;
bool parsingSuccessful = Json::parseFromStream(rbuilder, config_doc, &root, &errs);
if (!parsingSuccessful)
{
    // report to the user the failure and their locations in the document.
    std::cout  << "Failed to parse configuration\n"
               << errs;
    return;
}

// ...

Json::StreamWriterBuilder wbuilder;
// Configure the Builder, then ...
std::string outputConfig = Json::writeString(wbuilder, root);

A note on "comments"

Comments used to be supported in JSON but where removed for portability (C-like comments are not supported in Python). Since comments are useful in configuration/input file, this feature is preserved in jsoncpp.

Build instructions

The build instructions are located in the file README.md in the top-directory of the project.

What's New?

The description of latest changes can be found in NEWS.txt in the top-directory of the project.

TODO: Move to wiki.

Related links

• JSON Specification and alternate language implementations.
• YAML A data format designed for human readability.
• UTF-8 and Unicode FAQ.

Old project links

• https://sourceforge.net/projects/jsoncpp/ (aka 'json-cpp')
• http://jsoncpp.sourceforge.net
• http://sourceforge.net/projects/jsoncpp/files/
• http://jsoncpp.svn.sourceforge.net/svnroot/jsoncpp/trunk/
• http://jsoncpp.sourceforge.net/old.html

License

See file LICENSE in the top-directory of the project. Basically JsonCpp is licensed under MIT license, or public domain if desired and recognized in your jurisdiction.