c++：json 库 jsoncpp & CJsonObject
司空福
前言
jsoncpp 库
jsoncpp是一个可以与JSON进行交互的C++库
示例代码
1. 解析 json 对象
#include <iostream>
#include <string>
#include <jsoncpp/json/json.h>
using namespace std;
int main()
{
// 待解析的 json 字符串
string strJsonContent = "{\"role_id\": 1,\"occupation\": \"paladin\",\"camp\": \"alliance\"}";
// 待解析的结果
int nRoleDd = 0;
string strOccupation = "";
string strCamp = "";
// json 解析器
Json::Reader reader;
// json 根对象
Json::Value root;
// 将 strJsonContent 解析到 root
if (reader.parse(strJsonContent, root))
{
nRoleDd = root["role_id"].asInt();
strOccupation = root["occupation"].asString();
strCamp = root["camp"].asString();
}
cout << "role_id is: " << nRoleDd << endl;
cout << "occupation is: " << strOccupation << endl;
cout << "camp is: " << strCamp << endl;
return 0;
}
编译：g++ jsonstrparse.cpp -o jsonstrparse -ljsoncpp
2. 解析带有数组的 json
#include <iostream>
#include <string>
#include <jsoncpp/json/json.h>
using namespace std;
/*
{
"list" : [
{
"camp" : "alliance",
"occupation" : "paladin",
"role_id" : 1
},
{
"camp" : "alliance",
"occupation" : "Mage",
"role_id" : 2
}
],
"type" : "roles_msg",
"valid" : true
}
*/
int main()
{
// 待解析的 json 字符串
string strJsonContent = "{\"list\" : [{ \"camp\" : \"alliance\",\"occupation\" : \"paladin\",\"role_id\" : 1}, \
{\"camp\" : \"alliance\",\"occupation\" : \"Mage\",\"role_id\" : 2}],\"type\" : \"roles_msg\",\"valid\" : true}";
// 待解析的结果
string strType;
int nRoleDd = 0;
string strOccupation;
string strCamp;
// 对象
Json::Reader reader;
Json::Value root;
// 解析
if (reader.parse(strJsonContent, root))
{
// 【获取非数组内容】
strType = root["type"].asString();
cout << "type is: " << strType << endl;
// 【获取数组内容】
if (root["list"].isArray())
{
// 数组内有几个对象（size）
int nArraySize = root["list"].size();
for (int i = 0; i < nArraySize; i++)
{
nRoleDd = root["list"][i]["role_id"].asInt();
strOccupation = root["list"][i]["occupation"].asString();
strCamp = root["list"][i]["camp"].asString();
cout << "role_id is: " << nRoleDd << endl;
cout << "occupation is: " << strOccupation << endl;
cout << "camp is: " << strCamp << endl;
}
}
}
return 0;
}
写 json 文件
static void write_json(string f)
{
Json::Value root;
Json::FastWriter writer;
Json::Value person;
person["age"] = 28;
person["name"] = "sb";
root.append(person);
string json_file = writer.write(root);
ofstream ofs;
ofs.open(f);
assert(ofs.is_open());
ofs << json_file;
return;
}
注意
-
这里如果使用：
#include "json.h"代替#include <jsoncpp/json/json.h> & "#include<json/json.h>"(后两个均可编译过) -
在 编译时则会报错，很多错，看起来与 GLIBC 相关的，部分错误信息如下：
出现上述编译错误的原因是 jsoncpp 提供的头文件
/usr/local/include/json/features.h与 GLIBC 提供的头文件/usr/include/features.h有 冲突，如果我们使用 #include “json.h” 形式包含 json.h，则需要把头文件包含路径设置为 /usr/local/include/json/，此时，如果代码中有地方包含了 features.h（实际上，这是个很常用的头文件，很多地方都会包含此文件），则就会使用 json 提供的 features.h 了（而不是 GLIBC 提供的那个 features.h），从而导致 GLIBC 提供的 features.h 中的一些宏定义缺失（如上面的编译错误），进而导致编译失败。
CJsonObject 库
-
CJsonObject 是基于 cJSON 全新开发一个 C++ 版的 JSON 库
-
CJsonObject 的最大优势是 轻量（只有4个文件，拷贝到自己代码里即可，无须编译成库，且跨平台和编译器）
-
简单好用，开发效率极高，对多层嵌套json的读取和生成使用非常简单（大部分json解析库如果要访问多层嵌套json的最里层非常麻烦）。
示例代码
#include <string>
#include <iostream>
#include "../CJsonObject.hpp"
int main()
{
int iValue;
std::string strValue;
neb::CJsonObject oJson("{\"refresh_interval\":60,"
"\"dynamic_loading\":["
"{"
"\"so_path\":\"plugins/User.so\", \"load\":false, \"version\":1,"
"\"cmd\":["
"{\"cmd\":2001, \"class\":\"neb::CmdUserLogin\"},"
"{\"cmd\":2003, \"class\":\"neb::CmdUserLogout\"}"
"],"
"\"module\":["
"{\"path\":\"im/user/login\", \"class\":\"neb::ModuleLogin\"},"
"{\"path\":\"im/user/logout\", \"class\":\"neb::ModuleLogout\"}"
"]"
"},"
"{"
"\"so_path\":\"plugins/ChatMsg.so\", \"load\":false, \"version\":1,"
"\"cmd\":["
"{\"cmd\":2001, \"class\":\"neb::CmdChat\"}"
"],"
"\"module\":[]"
"}"
"]"
"}");
std::cout << oJson.ToString() << std::endl;
std::cout << "-------------------------------------------------------------------" << std::endl;
std::cout << oJson["dynamic_loading"][0]["cmd"][1]("class") << std::endl;
oJson["dynamic_loading"][0]["cmd"][0].Get("cmd", iValue);
std::cout << "iValue = " << iValue << std::endl;
oJson["dynamic_loading"][0]["module"][0].Get("path", strValue);
std::cout << "strValue = " << strValue << std::endl;
std::cout << "-------------------------------------------------------------------" << std::endl;
oJson.AddEmptySubObject("depend");
oJson["depend"].Add("nebula", "https://github.com/Bwar/Nebula");
oJson["depend"].AddEmptySubArray("bootstrap");
oJson["depend"]["bootstrap"].Add("BEACON");
oJson["depend"]["bootstrap"].Add("LOGIC");
oJson["depend"]["bootstrap"].Add("LOGGER");
oJson["depend"]["bootstrap"].Add("INTERFACE");
oJson["depend"]["bootstrap"].Add("ACCESS");
std::cout << oJson.ToString() << std::endl;
std::cout << "-------------------------------------------------------------------" << std::endl;
std::cout << oJson.ToFormattedString() << std::endl;
}
结果：
[bwar@nebula demo]$ ./CJsonObjectTest
{"refresh_interval":60,"dynamic_loading":[{"so_path":"plugins/User.so","load":false,"version":1,"cmd":[{"cmd":2001,"class":"neb::CmdUserLogin"},{"cmd":2003,"class":"neb::CmdUserLogout"}],"module":[{"path":"im/user/login","class":"neb::ModuleLogin"},{"path":"im/user/logout","class":"neb::ModuleLogout"}]},{"so_path":"plugins/ChatMsg.so","load":false,"version":1,"cmd":[{"cmd":2001,"class":"neb::CmdChat"}],"module":[]}]}
-------------------------------------------------------------------
neb::CmdUserLogout
iValue = 2001
strValue = im/user/login
-------------------------------------------------------------------
{"refresh_interval":60,"dynamic_loading":[{"so_path":"plugins/User.so","load":false,"version":1,"cmd":[{"cmd":2001,"class":"neb::CmdUserLogin"},{"cmd":2003,"class":"neb::CmdUserLogout"}],"module":[{"path":"im/user/login","class":"neb::ModuleLogin"},{"path":"im/user/logout","class":"neb::ModuleLogout"}]},{"so_path":"plugins/ChatMsg.so","load":false,"version":1,"cmd":[{"cmd":2001,"class":"neb::CmdChat"}],"module":[]}],"depend":{"nebula":"https://github.com/Bwar/Nebula","bootstrap":["BEACON","LOGIC","LOGGER","INTERFACE","ACCESS"]}}
-------------------------------------------------------------------
{
"refresh_interval": 60,
"dynamic_loading": [{
"so_path": "plugins/User.so",
"load": false,
"version": 1,
"cmd": [{
"cmd": 2001,
"class": "neb::CmdUserLogin"
}, {
"cmd": 2003,
"class": "neb::CmdUserLogout"
}],
"module": [{
"path": "im/user/login",
"class": "neb::ModuleLogin"
}, {
"path": "im/user/logout",
"class": "neb::ModuleLogout"
}]
}, {
"so_path": "plugins/ChatMsg.so",
"load": false,
"version": 1,
"cmd": [{
"cmd": 2001,
"class": "neb::CmdChat"
}],
"module": []
}],
"depend": {
"nebula": "https://github.com/Bwar/Nebula",
"bootstrap": ["BEACON", "LOGIC", "LOGGER", "INTERFACE", "ACCESS"]
}
}
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