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JsonCpp Documentation



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:

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


Notes: 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 was preserved.

Code example

Json::Value root;   // will contains the root value after parsing.
Json::Reader reader;
bool parsingSuccessful = reader.parse( config_doc, root );
if ( !parsingSuccessful )
    // report to the user the failure and their locations in the document.
    std::cout  << "Failed to parse configuration\n"
               << reader.getFormattedErrorMessages();

// 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 'encoding', 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();

Json::StyledWriter writer;
// Make a new JSON document for the configuration. Preserve original comments.
std::string outputConfig = writer.write( root );

// You can also use streams.  This will put the contents of any JSON
// stream at a particular sub-value, if you'd like.
std::cin >> root["subtree"];

// And you can write to a stream, using the StyledWriter automatically.
std::cout << root;

Build instructions

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

Permanent link to the latest revision of the file in subversion: latest README.txt


The sources can be downloaded from SourceForge download page.

The latest version of the source is available in the project's subversion repository: http://jsoncpp.svn.sourceforge.net/svnroot/jsoncpp/trunk/

To checkout the source, see the following instructions.

What's New?

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

Permanent link to the latest revision of the file in subversion: latest NEWS.txt

Project links

Related links


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.

Baptiste Lepilleur <blep@users.sourceforge.net>

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