C++第三方库jsoncpp超详细讲解

// Json数据对象类 -> 用于进行中间数据存储
class Json::Value
{
	// Value重载了[]和=，因此所有的赋值和获取数据都可以通过[]实现
	Value &operator=(const Value &other);

	// 简单的方式完成 val["姓名"] = "SnowK";
	Value& operator[](const std::string& key);
	Value& operator[](const char* key);

	// 移除元素
	Value removeMember(const char* key);

	// val["成绩"][0]
	const Value& operator[](ArrayIndex index) const; 

	// 添加数组元素val["成绩"].append(88); 
	Value& append(const Value& value);

	// 获取数组元素个数 val["成绩"].size();
	ArrayIndex size() const;

	// 转string   string name = val["name"].asString();
	std::string asString() const;

	// 转char*   char *name = val["name"].asCString();
	const char* asCString() const;

	// 转int  int age = val["age"].asInt();
	int asInt() const;              

	// 转float
	float asFloat() const;

	// 转 bool
	bool asBool() const;
};

//json序列化类，低版本用这个更简单
class JSON_API Writer 
{
	virtual std::string write(const Value& root) = 0;
}

class JSON_API FastWriter : public Writer 
{
	virtual std::string write(const Value& root);
}

class JSON_API StyledWriter : public Writer 
{
	virtual std::string write(const Value& root);
}

//json 序列化类，高版本推荐，如果用低版本的接口可能会有警告
class JSON_API StreamWriter 
{
	virtual int write(Value const& root, std::ostream* sout) = 0;
}

class JSON_API StreamWriterBuilder : public StreamWriter::Factory 
{
	virtual StreamWriter* newStreamWriter() const;
}

// json反序列化类，低版本用起来更简单
class JSON_API Reader 
{
	bool parse(const std::string& document, 
			   Value& root, bool collectComments = true);
}

// json反序列化类，高版本更推荐
class JSON_API CharReader 
{
	virtual bool parse(char const* beginDoc, char const* endDoc, 
					   Value* root, std::string* errs) = 0;
}

class JSON_API CharReaderBuilder : public CharReader::Factory 
{
	virtual CharReader* newCharReader() const;
}

int main()
{
    char name[] = "SnowK";
    int age = 18;
    float score[3] = {100, 99, 98};

    Json::Value stu;
    stu["Name"] = name;
    stu["Age"] = age;
    stu["Score"].append(score[0]);
    stu["Score"].append(score[1]);
    stu["Score"].append(score[2]);

    std::string str;
    if(Serialize(stu, str) == false)
    {
        return -1;
    }
    std::cout << str << std::endl;
    std::cout << "-------------------------------" << std::endl;

    Json::Value val;
    if(UnSerialize(str, val) == false)
    {
        return -1;
    }

    std::cout << val["Name"].asString() << std::endl;
    std::cout << val["Age"].asInt() << std::endl;
    for (int i = 0; i < val["Score"].size(); i++)
    {
        std::cout << val["Score"][i].asInt() << std::endl;
    }

    return 0;
}

bool Serialize(const Json::Value &val, std::string &dest)
{
    // 由Json::StreamWriterBuilder生产出Json::StreamWriter
    Json::StreamWriterBuilder swb;
    std::unique_ptr<Json::StreamWriter> sw(swb.newStreamWriter());

    // 通过Json::StreamWrite的write()进行序列化
    std::stringstream ss;
    if (sw->write(val, &ss) != 0)
    {
        std::cout << "Json序列化失败" << std::endl;
        return false;
    }

    dest = ss.str();

    return true;
}

bool UnSerialize(const std::string &src, Json::Value &val)
{
    Json::CharReaderBuilder crb;
    std::unique_ptr<Json::CharReader> cr(crb.newCharReader());

    std::string err;
    if (cr->parse(src.c_str(), src.c_str() + src.size(), &val, &err) == false)
    {
        std::cout << "json反序列化失败: " << err << std::endl;
        return false;
    }

    return true;
}