场景：要获取某个Json数据，但不知道Json数据的key。如：{"item_key1":"item_value1","item_key2":"item_value2","item_key3":"item_value3"}
解决：关键是如何获取到key，有了key，就可以获取到value了。可用通过getMemberNames函数获取key，之后通过key获取value

string strJson = "{"item_key1":"item_value1","item_key2":"item_value2","item_key3":"item_value3"}";
Json::Value valRoot; 
Json::Reader reader; 

        if (!reader.parse(strJson,valRoot))  
        {  
            return JSON_PARSE_ERR; 
        }  

        Json::Value::Members members; 
        members = valRoot.getMemberNames(); // 获取所有key的值
        for (Json::Value::Members::iterator iterMember = members.begin(); iterMember != members.end(); iterMember++) // 遍历每个key
        {  
            std::string strKey = *iterMember; 
            if (valRoot[strKey.c_str()].isString())  
            {  
                std::string strVal = valRoot[strKey.c_str()].asString(); 
                std::cout<<strKey.c_str()<<":"<<strVal.c_str()<<std::endl; 
            }  
            else if (valRoot[strKey.c_str()].isInt())  
            {  
                int iVal = valRoot[strKey.c_str()].asInt(); 
                std::cout<<strKey.c_str()<<":"<<iVal<<std::endl; 
            }  
            else if (valRoot[strKey.c_str()].isDouble())  
            {  
                double dVal = valRoot[strKey.c_str()].asDouble(); 
                std::cout<<strKey.c_str()<<":"<<dVal<<std::endl; 
            }  
            else  
            {  
                std::string strVal = valRoot[strKey.c_str()].toStyledString(); 
                std::cout<<strKey.c_str()<<":"<<strVal.c_str()<<std::endl; 
            }  
        }