使用boost属性树解析JSON [英] Parsing JSON with boost property tree

问题描述

我正在建立一个从themoviedb.com获取电影信息的应用程序。信息在JSON文件中提供。我试图使用boost属性树存储信息。但有一个小问题。

我通过以下代码说明问题：

  #include < vector> 
 #include< boost / property_tree / ptree.hpp> 
 #include< boost / property_tree / json_parser.hpp> 
 #include< boost / foreach.hpp> 
 
 using namespace std; 
使用boost :: property_tree :: ptree; 
 
 class single_t {
 int sID; 
 string sName; 
 public：
 void setID（int ID）{sID = ID;} 
 int getID（）{return sID;} 
 void setName（string Name）{sName = Name; } 
 string getName（）{return sName;} 
}; 
 
 typedef vector< single_t *> multiple_t; 
 
 class foo {
 string fTitle; 
 multiple_t fItems; 
 public：
 string getTitle（）{return fTitle;} 
 void setTitle（string Title）{fTitle = Title;} 
 multiple_t getItems（）{return fItems;} 
 void setItems（multiple_t Items）{fItems = Items;} 
 void setItems（single_t Item）{fItems.push_back（& Item）;} 
}; 
 
 int main（）{
 try {
 string response ={\title\：\Foo\，\items\ ：[{\id\：123，\name\：\test1\}，{\id\：456，\name\ \test2\}]}; 
 
 ptree pt; 
 stringstream ss; ss <<响应; 
 read_json（ss，pt）; 
 foo results; 
 results.setTitle（pt.get< string>（title））; 
 BOOST_FOREACH（ptree :: value_type& v，pt.get_child（items））{
 single_t result; 
 result.setID（v.second.get< int>（id））; 
 result.setName（v.second.get< string>（name））; 
 results.setItems（result）; 
} 
 cout<< Tilte：< results.getTitle（）<< endl 
 cout<< Items：<< endl 
 for（int i = 0; i！= results.getItems（）。size（）; i ++）{
 cout< \tID：<< results.getItems（）[i]  - > getID（）< endl 
 cout<< \tName：< results.getItems（）[i]  - > getName（）< endl 
} 
} 
 catch（exception& e）
 {
 cout< Exception：<< e.what（）; 
} 
 
} 
  

但是当我运行这个以下输出：

  Tilte：Foo 
项目：
 ID：456 
名称： test2 
 ID：456 
名称：test2 
  

m做错了？我想是在BOOST_FOREACH代码。

PS：使用Xcode 4.5.2与LLVM GCC 4.2编译器。

property_tree ，问题是，你尝试在向量中存储指向局部变量的指针。您可以通过值保存，或使用一些智能指针（例如 boost :: shared_ptr ）。

  void setItems（single_t Item）{fItems.push_back（& Item）;} 
  

退出此函数后，局部变量 Item 将被销毁，指针。

I'm building an application that gets movie information from themoviedb.com. The information is provided in a JSON file. I'm trying to store the information using boost property tree. But There is a little problem.

I illustrate the problem by the following code:

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

using namespace std;
using boost::property_tree::ptree;

class single_t{
    int             sID;
    string          sName;
public:
    void            setID(int ID){sID=ID;}
    int             getID(){return sID;}
    void            setName(string Name){sName=Name;}
    string          getName(){return sName;}
};

typedef vector<single_t*> multiple_t;

class foo{
    string          fTitle;
    multiple_t      fItems;
public:
    string          getTitle(){return fTitle;}
    void            setTitle(string Title){fTitle=Title;}
    multiple_t      getItems(){return fItems;}
    void            setItems(multiple_t Items){fItems = Items;}
    void            setItems(single_t Item){fItems.push_back(&Item);}
};

int main () {
    try{
        string response = "{\"title\":\"Foo\",\"items\":[{\"id\":123,\"name\":\"test1\"},{\"id\":456,\"name\":\"test2\"}]}";

        ptree pt;
        stringstream ss; ss << response;
        read_json(ss, pt);
        foo results;
        results.setTitle(pt.get<string>("title"));
        BOOST_FOREACH(ptree::value_type &v,pt.get_child("items")){
            single_t result;
            result.setID(v.second.get<int>("id"));
            result.setName(v.second.get<string>("name"));
            results.setItems(result);
        }
        cout << "Tilte: " << results.getTitle() << endl;
        cout << "Items:" << endl;
        for (int i=0; i!=results.getItems().size(); i++) {
            cout << "\tID: " << results.getItems()[i]->getID()<< endl;
            cout << "\tName: " << results.getItems()[i]->getName()<< endl;
        }
    }
    catch (exception& e)
    {
        cout << "Exception: " << e.what();
    }

}

But when I run this I get the following output:

Tilte: Foo
Items:
  ID: 456
  Name: test2
  ID: 456
  Name: test2

Does anyone know what I'm doing wrong? I guess it is in the BOOST_FOREACH code.

PS: Using Xcode 4.5.2 with LLVM GCC 4.2 Compiler.

解决方案

Problem is not with property_tree, problem is, that you try store pointer to local variable in vector. You can save by value, or use some smart pointer (for example boost::shared_ptr).

Problem:

void            setItems(single_t Item){fItems.push_back(&Item);}

After exit from this function, local variable Item will be destroyed, so you have dangling pointer.

这篇关于使用boost属性树解析JSON的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！