cpp-json

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cpp-json is licensed under the GNU General Public License, version 2 or later.

NOTE: version 2.2 will be the last to not require C++11.

There are a few different JSON parsing libraries out there. But cpp-json aims to be the simplest to use while still being efficient by using modern c++ techniques. Additionally, this library is header only making it trivial to include in existing projects.

Currently, the only active item on the TODO list is to better support Unicode. The parser can be given iterators referring to wide characters, but there is no runtime detection or endian-ness detection (yet)

However, Unicode is generally well supported in the form of \uXXXX encoding, including code points which require surrogate pairs. The resulting json::value object will contain the string, encoded as UTF-8 since it is stored in a std::string.

Of course special consideration is needed when displaying these strings if they do in fact contain non ASCII characters.

So, for example,

{"test1" : "\uD840\uDC8A"}

will correctly parse and the object's "test1" member will have the byte sequence: 0xF0 0xA0 0x82 0x8A

Here is a simple example of the usage of this library:

#include "cpp-json/json.h"
#include <fstream>
#include <iostream>

int main() {
	// open a file
	std::ifstream file("test.json");

	// json::parse can take two iterators or a std::istream
	json::value json = json::parse(file);

	// you can access objects like associative array's easily
	// the result is a json::value
	// ... though in real code you may want to check the type first ;-)
	auto servlets = json["web-app"]["servlet"];

	// when dealing with arrays, you can just use iterators, 
	// or feel free to use C++11 ranged-for
	const json::array &a = as_array(servlets);
	for(auto it = a.begin(); it != a.end(); ++it) {
        	const json::value &v = *it;
        	// all basic types (numbers, strings, booleans) can be converted 
        	// to a string
        	std::cout << to_string(v["servlet-name"]) << std::endl;
	}
}

You can also programmatically create json::value objects like this:

int main(int argc, char *argv[]) {
	auto arr = json::array {
		1,
		2,
		3,
		4,
		"Testing 1 2 3",
		json::object{
			{ "hello", 1234 },
			{ "world", 5678 }
		}
	};
	
	std::cout << stringify(arr) << std::endl;
}

Which of course results in a object representing the following JSON:

[
	1,
	2,
	3,
	4,
	"Testing 1 2 3", 
	{
		"hello" : 1234,
		"world" : 5678
	}
]

Finally, this library is very fast, when processing a 190 MB JSON file I randomly selected, parsing took no more than 18 seconds on my machine. For a Qt4 JSON parsing library, you can also checkout my other project: QJson4