C++ jsoncpp解析json字串
阿新 • • 發佈:2019-01-24
使用方法
下載原始碼解壓之後得到jsoncpp-src-0.5.0資料夾,我們只需要jsoncpp的標頭檔案和cpp檔案,其中jsonscpp的標頭檔案位於jsoncpp-src-0.5.0\include\json,jsoncpp的cpp檔案位於jsoncpp-src-0.5.0\src\lib_json。
json: json操作所需的標頭檔案,此資料夾名字不能修改,因為lib_json目錄中所對應的.cpp裡面包含標頭檔案形式是這樣:
#include <json/xxx.h>
lib_json:json操作所需的cpp檔案,此資料夾名字可根據需要自行命名。
把json和lib_json拷貝出來放在你需要編寫程式碼的目錄中(注意:json 和 lib_json 要在同一級目錄):
從字串中讀取json
#include <string>
#include <json/json.h>
#include <iostream>
#include <fstream>
using namespace std;
void readStrJson(); //從字串中讀取JSON
void readStrProJson(); //從字串中讀取JSON(內容複雜些)
int main(int argc, char *argv[])
{
readStrJson();
cout << "\n\n";
readStrProJson();
return 0;
}
//從字串中讀取JSON
void readStrJson()
{
//字串
const char* str =
"{\"praenomen\":\"Gaius\",\"nomen\":\"Julius\",\"cognomen\":\"Caezar\","
"\"born\":-100,\"died\":-44}";
/*
//json內容如下:
{
"praenomen":"Gaius",
"nomen":"Julius",
"cognomen":"Caezar",
"born":-100,
"died":-44
}
*/
Json::Reader reader;
Json::Value root;
//從字串中讀取資料
if(reader.parse(str,root))
{
string praenomen = root["praenomen"].asString();
string nomen = root["nomen"].asString();
string cognomen = root["cognomen"].asString();
int born = root["born"].asInt();
int died = root["died"].asInt();
cout << praenomen + " " + nomen + " " + cognomen
<< " was born in year " << born
<< ", died in year " << died << endl;
}
}
//從字串中讀取JSON(內容複雜些)
void readStrProJson()
{
string strValue = "{\"name\":\"json\",\"array\":[{\"cpp\":\"jsoncpp\"},{\"java\":\"jsoninjava\"},{\"php\":\"support\"}]}";
/*
//json內容如下:
{
"name": "json″,
"array": [
{
"cpp": "jsoncpp"
},
{
"java": "jsoninjava"
},
{
"php": "support"
}
]
}
*/
Json::Reader reader;
Json::Value value;
if (reader.parse(strValue, value))
{
string out = value["name"].asString();
cout << out << endl;
const Json::Value arrayObj = value["array"];
for (unsigned int i = 0; i < arrayObj.size(); i++)
{
if (!arrayObj[i].isMember("cpp"))
continue;
out = arrayObj[i]["cpp"].asString();
cout << out;
if (i != (arrayObj.size() - 1))
cout << endl;
}
}
}
從檔案中讀取JSON
#include <string>
#include <json/json.h>
#include <iostream>
#include <fstream>
using namespace std;
void readFileJson(); //從檔案中讀取JSON,一個儲存了JSON格式字串的檔案
int main(int argc, char *argv[])
{
readFileJson();
return 0;
}
//從檔案中讀取JSON
void readFileJson()
{
Json::Reader reader;
Json::Value root;
//從檔案中讀取,保證當前檔案有test.json檔案
ifstream in("test.json", ios::binary);
//in.open("test.json", ios::binary);
if( !in.is_open() )
{
cout << "Error opening file\n";
return;
}
/*
//test.json內容如下:
{
"name":"Tsybius",
"age":23,
"sex_is_male":true,
"partner":
{
"partner_name":"Galatea",
"partner_age":21,
"partner_sex_is_male":false
},
"achievement":["ach1","ach2","ach3"]
}
*/
if(reader.parse(in,root))
{
//讀取根節點資訊
string name = root["name"].asString();
int age = root["age"].asInt();
bool sex_is_male = root["sex_is_male"].asBool();
cout << "My name is " << name << endl;
cout << "I'm " << age << " years old" << endl;
cout << "I'm a " << (sex_is_male ? "man" : "woman") << endl;
//讀取子節點資訊
string partner_name = root["partner"]["partner_name"].asString();
int partner_age = root["partner"]["partner_age"].asInt();
bool partner_sex_is_male = root["partner"]["partner_sex_is_male"].asBool();
cout << "My partner's name is " << partner_name << endl;
cout << (partner_sex_is_male ? "he" : "she") << " is "
<< partner_age << " years old" << endl;
//讀取陣列資訊
cout << "Here's my achievements:" << endl;
for(unsigned int i = 0; i < root["achievement"].size(); i++)
{
string ach = root["achievement"][i].asString();
cout << ach << '\t';
}
cout << endl;
cout << "Reading Complete!" << endl;
}
else
{
cout << "parse error\n" << endl;
}
in.close();
}
test.json檔案內容如下:
{
"name":"Mike Jiang",
"age":23,
"sex_is_male":true,
"partner":
{
"partner_name":"Galatea",
"partner_age":21,
"partner_sex_is_male":false
},
"achievement":["ach1","ach2","ach3"]
}
把資訊儲存為JSON格式
#include <string>
#include <json/json.h>
#include <iostream>
#include <fstream>
using namespace std;
void writeFileJson();//將資訊儲存為JSON格式
int main(int argc, char *argv[])
{
writeFileJson();
return 0;
}
//將資訊儲存為JSON格式
void writeFileJson()
{
//根節點
Json::Value root;
//根節點屬性
root["name"] = Json::Value("Mike Jiang");
root["age"] = Json::Value(23);
root["sex_is_male"] = Json::Value(true);
//子節點
Json::Value partner;
//子節點屬性
partner["partner_name"] = Json::Value("Galatea");
partner["partner_age"] = Json::Value(21);
partner["partner_sex_is_male"] = Json::Value(false);
//子節點掛到根節點上
root["partner"] = Json::Value(partner);
//陣列形式
root["achievement"].append("ach1");
root["achievement"].append("ach2");
root["achievement"].append("ach3");
//直接輸出
cout << "FastWriter:" << endl;
Json::FastWriter fw;
cout << fw.write(root) << endl << endl;
//縮排輸出
cout << "StyledWriter:" << endl;
Json::StyledWriter sw;
cout << sw.write(root) << endl << endl;
//輸出到檔案
ofstream os;
os.open("demo.json");
os << sw.write(root);
os.close();
/*
//json檔案內容如下:
{
"achievement" : [ "ach1", "ach2", "ach3" ],
"age" : 23,
"name" : "Mike Jiang",
"partner" : {
"partner_age" : 21,
"partner_name" : "Galatea",
"partner_sex_is_male" : false
},
"sex_is_male" : true
}
*/
}