JSON for Modern C 是一个由德国大牛 nlohmann 编写的在 C 下使用的 JSON 库。
具有以下特点
直观的语法
整个代码由一个头文件组成 json.hpp,没有子项目,没有依赖关系,没有复杂的构建系统,使用起来非常方便
使用 C++ 11 标准编写
使用 json 像使用 STL 容器一样
STL 和 json 容器之间可以相互转换
严谨的测试:所有类都经过严格的单元测试,覆盖了 100% 的代码,包括所有特殊的行为。此外,还检查了 Valgrind 是否有内存泄漏。为了保持高质量,该项目遵循核心基础设施倡议(CII)的最佳实践
示例代码
假设要创建如下的 JSON 对象
{ "pi": 3.141, "happy": true, "name": "Niels", "nothing": null, "answer": { "everything": 42 }, "list": [1, 0, 2], "object": { "currency": "USD", "value": 42.99 } }
使用这个 JSON 库,可以这样写
// create an empty structure (null) json j; // add a number that is stored as double (note the implicit conversion of j to an object) j["pi"] = 3.141; // add a Boolean that is stored as bool j["happy"] = true; // add a string that is stored as std::string j["name"] = "Niels"; // add another null object by passing nullptr j["nothing"] = nullptr; // add an object inside the object j["answer"]["everything"] = 42; // add an array that is stored as std::vector (using an initializer list) j["list"] = { 1, 0, 2 }; // add another object (using an initializer list of pairs) j["object"] = { {"currency", "USD"}, {"value", 42.99} }; // instead, you could also write (which looks very similar to the JSON above) json j2 = { {"pi", 3.141}, {"happy", true}, {"name", "Niels"}, {"nothing", nullptr}, {"answer", { {"everything", 42} }}, {"list", {1, 0, 2}}, {"object", { {"currency", "USD"}, {"value", 42.99} }} };
请注意,在所有上述情况下,不需要“告诉”编译器要使用哪个 JSON 值。如果想要明确或表达一些边缘的情况,可以使用 json::array 和 json::object
json::array
json::object
// a way to express the empty array [] json empty_array_explicit = json::array(); // ways to express the empty object {} json empty_object_implicit = json({}); json empty_object_explicit = json::object(); // a way to express an _array_ of key/value pairs [["currency", "USD"], ["value", 42.99]] json array_not_object = json::array({ {"currency", "USD"}, {"value", 42.99} });