windows客户端开发--使用json11解析json

类似xml，JSON(JavaScript Object Notation) 是一种轻量级的数据交换格式。

json11是适用于c++11的一个轻量级的库，用于解析json.

什么是json?
JSON is short for JavaScript Object Notation, and is a way to store information in an organized, easy-to-access manner. In a nutshell, it gives us a human-readable collection of data that we can access in a really logical manner.

json如何存储？

var jason = {
    "age" : "24",
    "hometown" : "Missoula, MT",
    "gender" : "male"
};

将json存为数组

var family = [{
    "name" : "Jason",
    "age" : "24",
    "gender" : "male"
},
{
    "name" : "Kyle",
    "age" : "21",
    "gender" : "male"
}];

使用json11进行解析

#include <string.h>
#include <cstdio>
#include <iostream>
#include <sstream>
#include "lasote/json11/json11.hpp"
#include <cassert>
#include <list>
#include <set>
#include <unordered_map>

using namespace json11;
using std::string;


int main(int argc, char **argv) {


    // STRING TO JSON
    const string simple_test =
        R"({"k1":"v1", "k2":42, "k3":["a",123,true,false,null]})";

    string err;
    auto json = Json::parse(simple_test, err);
    std::cout << "k1: " << json["k1"].string_value() << "\n";
    std::cout << "k3: " << json["k3"].dump() << "\n";


    // JSON FROM LITERAL
    Json obj = Json::object({
        { "k1", "v1" },
        { "k2", 42.0 },
        { "k3", Json::array({ "a", 123.0, true, false, nullptr }) },
    });

    std::cout << "obj: " << obj.dump() << "\n";

    // CUSTOM CLASS JSON ENCODE
    class Point {
    public:
        int x;
        int y;
        Point (int x, int y) : x(x), y(y) {}
        Json to_json() const { return Json::array { x, y }; }
    };

    std::vector<Point> points = { { 1, 2 }, { 10, 20 }, { 100, 200 } };
    std::string points_json = Json(points).dump();
    printf("%s\n", points_json.c_str());
}

josn11源码头文件

class __declspec(dllexport) Json final {
public:
    // Types
    enum Type {
        NUL, NUMBER, BOOL, STRING, ARRAY, OBJECT
    };

    // Array and object typedefs
    typedef std::vector<Json> array;
    typedef std::map<std::string, Json> object;

    // Constructors for the various types of JSON value.
    Json() noexcept;                // NUL
    Json(std::nullptr_t) noexcept;  // NUL
    Json(double value);             // NUMBER
    Json(int value);                // NUMBER
    Json(bool value);               // BOOL
    Json(const std::string &value); // STRING
    Json(std::string &&value);      // STRING
    Json(const char * value);       // STRING
    Json(const array &values);      // ARRAY
    Json(array &&values);           // ARRAY
    Json(const object &values);     // OBJECT
    Json(object &&values);          // OBJECT

    // Implicit constructor: anything with a to_json() function.
    template <class T, class = decltype(&T::to_json)>
    Json(const T & t) : Json(t.to_json()) {}

    // Implicit constructor: map-like objects (std::map, std::unordered_map, etc)
    template <class M, typename std::enable_if<
        std::is_constructible<std::string, typename M::key_type>::value
        && std::is_constructible<Json, typename M::mapped_type>::value,
            int>::type = 0>
    Json(const M & m) : Json(object(m.begin(), m.end())) {}

    // Implicit constructor: vector-like objects (std::list, std::vector, std::set, etc)
    template <class V, typename std::enable_if<
        std::is_constructible<Json, typename V::value_type>::value,
            int>::type = 0>
    Json(const V & v) : Json(array(v.begin(), v.end())) {}

    // This prevents Json(some_pointer) from accidentally producing a bool. Use
    // Json(bool(some_pointer)) if that behavior is desired.
    Json(void *) = delete;

    // Accessors
    Type type() const;

    bool is_null()   const { return type() == NUL; }
    bool is_number() const { return type() == NUMBER; }
    bool is_bool()   const { return type() == BOOL; }
    bool is_string() const { return type() == STRING; }
    bool is_array()  const { return type() == ARRAY; }
    bool is_object() const { return type() == OBJECT; }

    // Return the enclosed value if this is a number, 0 otherwise. Note that json11 does not
    // distinguish between integer and non-integer numbers - number_value() and int_value()
    // can both be applied to a NUMBER-typed object.
    double number_value() const;
    int int_value() const;

    // Return the enclosed value if this is a boolean, false otherwise.
    bool bool_value() const;
    // Return the enclosed string if this is a string, "" otherwise.
    const std::string &string_value() const;
    // Return the enclosed std::vector if this is an array, or an empty vector otherwise.
    const array &array_items() const;
    // Return the enclosed std::map if this is an object, or an empty map otherwise.
    const object &object_items() const;

    // Return a reference to arr[i] if this is an array, Json() otherwise.
    const Json & operator[](size_t i) const;
    // Return a reference to obj[key] if this is an object, Json() otherwise.
    const Json & operator[](const std::string &key) const;

    // Serialize.
    void dump(std::string &out) const;
    std::string dump() const {
        std::string out;
        dump(out);
        return out;
    }

    // Parse. If parse fails, return Json() and assign an error message to err.
    static Json parse(const std::string & in, std::string & err);
    static Json parse(const char * in, std::string & err) {
        if (in) {
            return parse(std::string(in), err);
        } else {
            err = "null input";
            return nullptr;
        }
    }
    // Parse multiple objects, concatenated or separated by whitespace
    static std::vector<Json> parse_multi(const std::string & in, std::string & err);

    bool operator== (const Json &rhs) const;
    bool operator<  (const Json &rhs) const;
    bool operator!= (const Json &rhs) const { return !(*this == rhs); }
    bool operator<= (const Json &rhs) const { return !(rhs < *this); }
    bool operator>  (const Json &rhs) const { return  (rhs < *this); }
    bool operator>= (const Json &rhs) const { return !(*this < rhs); }

    /* has_shape(types, err) * * Return true if this is a JSON object and, for each item in types, has a field of * the given type. If not, return false and set err to a descriptive message. */
    typedef std::initializer_list<std::pair<std::string, Type>> shape;
    bool has_shape(const shape & types, std::string & err) const;

private:
    std::shared_ptr<JsonValue> m_ptr;
};

// Internal class hierarchy - JsonValue objects are not exposed to users of this API.
class JsonValue {
protected:
    friend class Json;
    friend class JsonInt;
    friend class JsonDouble;
    virtual Json::Type type() const = 0;
    virtual bool equals(const JsonValue * other) const = 0;
    virtual bool less(const JsonValue * other) const = 0;
    virtual void dump(std::string &out) const = 0;
    virtual double number_value() const;
    virtual int int_value() const;
    virtual bool bool_value() const;
    virtual const std::string &string_value() const;
    virtual const Json::array &array_items() const;
    virtual const Json &operator[](size_t i) const;
    virtual const Json::object &object_items() const;
    virtual const Json &operator[](const std::string &key) const;
    virtual ~JsonValue() {}
};

} // namespace json11

哦对了，写到现在连个windows还没提到呢？难道博主是挂鸡头卖鸭头？

错。在客户端开发中，pc也好 移动也好，总是需要服务器返回的数据。
这个response往往就是json类型的，所以我们做客户端的需要对json对象进行解析，然后进行使用~~