Question

C++解析Json字符串问题！

问题出错在这一句代码上
cout<<root["results"][0]["currentCity"].asString()<<endl;
vc提示 error C2593: 'operator [' is ambiguous
下图是要解析的Json格式的字符串部分截图

Answer 1

一、从字符串中读取JSON
#include <iostream>
#include "json/json.h"
using namespace std;
int main()
{
//字符串
const char * str =
"{\"praenomen\":\"Gaius\",\"nomen\":\"Julius\",\"cognomen\":\"Caezar\","
"\"born\":-100,\"died\":-44}" ;
Json::Reader reader;
Json::Value root;
//从字符串中读取数据
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;
}
return 0;
}

makefile文件
LIB=-L /usr/local/lib/libjson/ -ljson_linux- gcc -4.4.7_libmt
a: a.o
g++ -o a -std=c++0x a.o $(LIB)
a.o: a.cpp
g++ -c a.cpp
clean:
rm -rf a.o a

二、从文件中读取JSON
PersonalInfo.json（一个存储了JSON格式字符串的文件）

{
"name" : "Tsybius" ,
"age" :23,
"sex_is_male" : true ,
"partner" :
{
"partner_name" : "Galatea" ,
"partner_age" :21,
"partner_sex_is_male" : false
},
"achievement" :[ "ach1" , "ach2" , "ach3" ]
}
#include <iostream>
#include <fstream>
#include "json/json.h"
using namespace std;
int main()
{
Json::Reader reader;
Json::Value root;
//从文件中读取
ifstream is;
is.open( "PersonalInfo.json" , ios::binary);
if (reader.parse(is,root))
{
//读取根节点信息
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;
//读取子节点信息
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;
//读取数组信息
cout << "Here's my achievements:" << endl;
for ( int i = 0; i < root[ "achievement" ].size(); i++)
{
string ach = root[ "achievement" ][i].asString();
cout << ach << '\t' ;
}
cout << endl;
cout << "Reading Complete!" << endl;
}
is.close();
return 0;
}

makefile
?
LIB=-L /usr/local/lib/libjson/ -ljson_linux- gcc -4.4.7_libmt
a: a.o
g++ -o a -std=c++0x a.o $(LIB)
a.o: a.cpp
g++ -c a.cpp
clean:
rm -rf a.o a

三、将信息保存为JSON格式
a.cpp

#include <iostream>
#include <fstream>
#include "json/json.h"
using namespace std;
int main()
{
//根节点
Json::Value root;
//根节点属性
root[ "name" ] = Json::Value( "Tsybius" );
root[ "age" ] = Json::Value(23);
root[ "sex_is_male" ] = Json::Value( true );
//子节点
Json::Value partner;
//子节点属性
partner[ "partner_name" ] = Json::Value( "Galatea" );
partner[ "partner_age" ] = Json::Value(21);
partner[ "partner_sex_is_male" ] = Json::Value( false );
//子节点挂到根节点上
root[ "partner" ] = Json::Value(partner);
//数组形式
root[ "achievement" ].append( "ach1" );
root[ "achievement" ].append( "ach2" );
root[ "achievement" ].append( "ach3" );

//直接输出
cout << "FastWriter:" << endl;
Json::FastWriter fw;
cout << fw.write(root) << endl << endl;
//缩进输出
cout << "StyledWriter:" << endl;
Json::StyledWriter sw;
cout << sw.write(root) << endl << endl;

//输出到文件
ofstream os;
os.open( "PersonalInfo" );
os << sw.write(root);
os.close();
return 0;
}

makefile
LIB=-L /usr/local/lib/libjson/ -ljson_linux- gcc -4.4.7_libmt
a: a.o
g++ -o a -std=c++0x a.o $(LIB)
a.o: a.cpp
g++ -c a.cpp
clean:
rm -rf a.o a

{
"achievement" : [ "ach1" , "ach2" , "ach3" ],
"age" : 23,
"name" : "Tsybius" ,
"partner" : {
"partner_age" : 21,
"partner_name" : "Galatea" ,
"partner_sex_is_male" : false
},
"sex_is_male" : true
}

Answer 2

试试改成：

cout<<root[string("results")][0][string("currentCity")].asString()<<endl;