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\section _intro Introduction
<a HREF="">JSON (JavaScript Object Notation)</a>
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 }
\section _features Features
- read and write JSON document
- attach C and C++ style comments to element during parsing
- rewrite JSON document preserving original comments
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
\section _example 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;
\section _pbuild Build instructions
The build instructions are located in the file
<a HREF="README.txt">README.txt</a> in the top-directory of the project.
Permanent link to the latest revision of the file in subversion:
<a HREF="">latest README.txt</a>
\section _pdownload Download
The sources can be downloaded from
<a HREF="">SourceForge download page</a>.
The latest version of the source is available in the project's subversion repository:
<a HREF=""></a>
To checkout the source, see the following
<a HREF="">instructions</a>.
\section _news What's New?
The description of latest changes can be found in
<a HREF="NEWS.txt">NEWS.txt</a> in the top-directory of the project.
Permanent link to the latest revision of the file in subversion:
<a HREF="">latest NEWS.txt</a>
\section _plinks Project links
- <a HREF="">json-cpp home</a>
- <a HREF="">json-cpp sourceforge project</a>
\section _rlinks Related links
- <a HREF="">JSON</a> Specification and alternate language implementations.
- <a HREF="">YAML</a> A data format designed for human readability.
- <a HREF="">UTF-8 and Unicode FAQ</a>.
\section _license License
See file <a HREF="LICENSE">LICENSE</a> in the top-directory of the project.
Basically JsonCpp is licensed under MIT license, or public domain if desired
and recognized in your jurisdiction.
\author Baptiste Lepilleur <>