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JSON (JavaScript Object Notation) is a lightweight data-interchange format.
Here is an example of JSON data:
{ "encoding" : "UTF-8", "plug-ins" : [ "python", "c++", "ruby" ], "indent" : { "length" : 3, "use_space": true } }
JsonCpp supports comments as meta-data:
// Configuration options { // Default encoding for text "encoding" : "UTF-8", // Plug-ins loaded at start-up "plug-ins" : [ "python", "c++", // trailing comment "ruby" ], // Tab indent size // (multi-line comment) "indent" : { /*embedded comment*/ "length" : 3, "use_space": true } }
Notes: Comments used to be supported in JSON but were removed for portability (C like comments are not supported in Python). Since comments are useful in configuration/input file, this feature was preserved.
Json::Value root; // 'root' will contain the root value after parsing. std::cin >> root; // You can also read into a particular sub-value. std::cin >> root["subtree"]; // Get the value of the member of root named 'encoding', // and 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"]; // Iterate over the sequence elements. for ( int index = 0; index < plugins.size(); ++index ) loadPlugIn( plugins[index].asString() ); // Try other datatypes. Some are auto-convertible to others. foo::setIndentLength( root["indent"].get("length", 3).asInt() ); foo::setIndentUseSpace( root["indent"].get("use_space", true).asBool() ); // Since Json::Value has an implicit constructor for all value types, it is not // necessary to explicitly construct the Json::Value object. root["encoding"] = foo::getCurrentEncoding(); root["indent"]["length"] = foo::getCurrentIndentLength(); root["indent"]["use_space"] = foo::getCurrentIndentUseSpace(); // If you like the defaults, you can insert directly into a stream. std::cout << root; // Of course, you can write to `std::ostringstream` if you prefer. // If desired, remember to add a linefeed and flush. std::cout << std::endl;
Configure *builders* to create *readers* and *writers*. For configuration, we use our own `Json::Value` (rather than standard setters/getters) so that we can add features without losing binary-compatibility.
// For convenience, use `writeString()` with a specialized builder. Json::StreamWriterBuilder wbuilder; wbuilder["indentation"] = "\t"; std::string document = Json::writeString(wbuilder, root); // Here, using a specialized Builder, we discard comments and // record errors as we parse. Json::CharReaderBuilder rbuilder; rbuilder["collectComments"] = false; std::string errs; bool ok = Json::parseFromStream(rbuilder, std::cin, &root, &errs);
Yes, compile-time configuration-checking would be helpful, but `Json::Value` lets you write and read the builder configuration, which is better! In other words, you can configure your JSON parser using JSON.
CharReaders and StreamWriters are not thread-safe, but they are re-usable.
Json::CharReaderBuilder rbuilder; cfg >> rbuilder.settings_; std::unique_ptr<Json::CharReader> const reader(rbuilder.newCharReader()); reader->parse(start, stop, &value1, &errs); // ... reader->parse(start, stop, &value2, &errs); // etc.
The build instructions are located in the file README.md in the top-directory of the project.
The latest version of the source is available in the project's GitHub repository: jsoncpp
The description of latest changes can be found in the NEWS wiki .
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.
1.6.2