c++ 解析json

 c++解析json有很库，boost，jsoncpp等。

boost解析json

要包含头文件：

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

/*
g++ -o json_test json_test.cpp 
*/
#include<boost/property_tree/ptree.hpp>
#include<boost/property_tree/json_parser.hpp>

#include<string>
#include<sstream>
#include<fstream>
using namespace std;

using namespace boost::property_tree;
void create_json()
{
     ptree pt_1,pt_11,pt_12;
    
    pt_11.put("id","3445");
    pt_11.put("age",29);
    pt_11.put("name","chen");    
    
    pt_12.push_back(make_pair("",pt_11));
    pt_12.push_back(make_pair("",pt_11));

    //replace or create child node "data"
    pt_1.put_child("data",pt_12);    
    
    ostringstream os;
    write_json(os,pt_1);
    
    
    cout<<os.str()<<endl;
/* 生成文件 ofstream.h

ofstream myOfstream("json.txt");
myOfstream<<os.str();
myOfstream.close();

*/
     
}
int main()
{
     
    create_json();
}

输出：

{
    "data": [
        {
            "id": "3445",
            "age": "29",
            "name": "chen"
        },
        {
            "id": "3445",
            "age": "29",
            "name": "chen"
        }
    ]
}

解析上面的：

void parse_json()
{
    ifstream in("json.txt");
    vector<string> vecId;
    vector<int> vecAge;
    vector<string> vecName;
    
    ptree pt,p1,p2;
    read_json<ptree>(in,pt);
    p1=pt.get_child("data");
    for(ptree::iterator it=p1.begin();it!=p1.end();it++)
    {
        p2=it->second;//first为空
        string idStr=p2.get<string>("id");
        vecId.push_back(idStr);
        
        int age=p2.get<int>("age");
        vecAge.push_back(age);
        
        string nameStr=p2.get<string>("name");
        vecName.push_back(nameStr);
        
    }
    
    copy(vecId.begin(),vecId.end(),ostream_iterator<string>(cout,"	"));
    copy(vecAge.begin(),vecAge.end(),ostream_iterator<int>(cout,"	"));
    copy(vecName.begin(),vecName.end(),ostream_iterator<string>(cout,"	"));
    
}

一篇文章：

接着，将上面这串Json赋给一个变量

string strJson ={ "people": [ { "firstName": "Brett", "lastName":"McLaughlin", "email": "aaaa" }, 　

{ "firstName": "Jason", "lastName":"Hunter", "email": "bbbb"}, 　　

{ "firstName": "Elliotte", "lastName":"Harold", "email": "cccc" } 　　]} 

注：在C++中需要在“前面加入进行转意。

接下来，给程序增加如下变量：

string stra,strc;
vector<string> vecStr;
ptree pt,p1,p2;
stringstream stream;

下面的程序是解析Json

    stream << strJson;
    read_json<ptree>( stream, pt);
    p1 = pt.get_child("people");
    for (ptree::iterator it = p1.begin(); it != p1.end(); ++it)
    {
        p2 = it->second; //first为空
        stra = p2.get<string>("firstName");
        vecStr.push_back(stra);   
    }

这样，vecStr中就有三个值，Brett，Jason，Elliotte，Json解析完成。

对于下面这样的Json格式，

{ "programmers": [ { "firstName": "Brett", "lastName":"McLaughlin", "email": "aaaa" }, 　　{ "firstName": "Jason", "lastName":"Hunter", "email": "bbbb" }, 　　{ "firstName": "Elliotte", "lastName":"Harold", "email": "cccc" }　　],　　"authors": [ 　　{ "firstName": "Isaac", "lastName": "Asimov", "genre": "science fiction" }, 　　{ "firstName": "Tad", "lastName": "Williams", "genre": "fantasy" }, 　　{ "firstName": "Frank", "lastName": "Peretti", "genre": "christian fiction" } 　　], 　　"musicians": [ 　　{ "firstName": "Eric", "lastName": "Clapton", "instrument": "guitar" }, 　　{ "firstName": "Sergei", "lastName": "Rachmaninoff", "instrument": "piano" } 　　] } 

就需要对上面的这两句程序稍微改动下就行了。

 p1 = pt.get_child("programmers");

stra = p2.get<string>("firstName");

对比一下，发现什么不同了吗？就是将参数稍微修改了一下。如果要得到musicians里面的firstName呢？就只要将p1 = pt.get_child("programmers");中的参数改成musicians；

如果Json里面嵌套了Json，则需要增加一个Ptree 变量pt3,pt4.使

p3 = p2.get_child("嵌套的值");

for (ptree::iterator ita = p3.begin(); ita != p3.end(); ++ita)
         {
             p4 = ita->second;
             strc = p4.get<string>("markerItemLink");            
         }

相关源代码请访问地址

http://download.csdn.net/detail/yqmfly/3729591

 http://blog.csdn.net/yqmfly/article/details/6914590

更多：

http://blog.csdn.net/dotphoenix/article/details/27081377

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jsoncpp 是比较出名的 C++ JSON 解析库。在 JSON官网也是首推的。下载地址为：http://sourceforge.net/projects/jsoncpp 。新的地址：https://github.com/open-source-parsers/jsoncpp。