Home (original) (raw)

branch	Travis CI	AppVeyor
master
0.y.z

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:

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

And here it is with comments:

// Configuration options { // Default encoding for text "my-encoding" : "UTF-8",

// Plug-ins loaded at start-up
"my-plug-ins" : [
    "python",
    "c++",
    "ruby"
    ],
    
// Tab indent size
"my-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/json.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 'my-encoding', return 'UTF-32' if there is no // such member. std::string my_encoding = root.get("my-encoding", "UTF-32" ).asString();

// Get the value of the member of root named 'my-plug-ins'; return a 'null' value if // there is no such member. const Json::Value my_plugins = root["my-plug-ins"]; for ( int index = 0; index < my_plugins.size(); ++index ) // Iterates over the sequence elements. yourlib::loadPlugIn( my_plugins[index].asString() );

yourlib::setIndentLength( root["my-indent"].get("length", 3).asInt() ); yourlib::setIndentUseSpace( root["my-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"] = yourlib::getCurrentEncoding(); root["indent"]["length"] = yourlib::getCurrentIndentLength(); root["indent"]["use_space"] = yourlib::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

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

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

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

For other build systems, see Building.

What's New?

See the release notes.

Older news can be found in News.

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

Old project links

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.