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Question

JSON文件我有一個這樣的文件：

[data.json]

{ 
    "electron": { 
     "pos": [0,0,0], 
     "vel": [0,0,0] 
    }, 

    "proton": { 
     "pos": [1,0,0], 
     "vel": [0,0.1,0] 
    }, 

    "proton": { 
     "pos": [-1,0,0], 
     "vel": [0,-0.1,-0.1] 
    } 
} 

如何創建粒子從解析該文件的向量。據我瞭解，我需要使用boost讀取文件，並將字符串（行）讀入向量，然後解析向量的內容。

類粒子是這樣的：

class Particle 
{ 

    private: 
    particle_type mtype; // particle_type is an enum 
    vector<double> mPos; 
    vector<double> mVel; 
}; 

爲的get/set其它方法在課堂上省略。

基本上我想幫助創建一個vector<Particle>與正確的位置和速度數據和particle_type數據解析到它。提前致謝。

碼主：

int main(){ 

    boost::property_tree::ptree pt; 
    boost::property_tree::read_json("data.json", pt); 
} 

Answer 1

您可以用下面的代碼迭代：

boost::property_tree::basic_ptree<std::string,std::string>::const_iterator iter = pt.begin(),iterEnd = pt.end(); 
for(;iter != iterEnd;++iter) 
{ 
    iter->first; // Your key, at this level it will be "electron", "proton", "proton" 
    iter->second; // The object at each step {"pos": [0,0,0], "vel": [0,0,0]}, etc. 
} 

希望它可以幫助

Answer 2

我修改你的JSON一點。稍微未經測試的代碼。

{ 
    "particles": [ 
     { 
      "electron": { 
       "pos": [ 
        0, 
        0, 
        0 
       ], 
       "vel": [ 
        0, 
        0, 
        0 
       ] 
      }, 
      "proton": { 
       "pos": [ 
        -1, 
        0, 
        0 
       ], 
       "vel": [ 
        0, 
        -0.1, 
        -0.1 
       ] 
      } 
     } 
    ] 
} 

...

#ifdef _MSC_VER 
#include <boost/config/compiler/visualc.hpp> 
#endif 
#include <boost/property_tree/ptree.hpp> 
#include <boost/property_tree/json_parser.hpp> 
#include <boost/foreach.hpp> 
#include <cassert> 
#include <exception> 
#include <iostream> 
#include <sstream> 
#include <string> 

int main() 
{ 
    try 
    { 
     std::stringstream ss; 
     // send your JSON above to the parser below, but populate ss first 


     boost::property_tree::ptree pt; 
     boost::property_tree::read_json(ss, pt); 

     BOOST_FOREACH(boost::property_tree::ptree::value_type &v, pt.get_child("particles.electron")) 
     { 
      assert(v.first.empty()); // array elements have no names 
      std::cout << v.second.data() << std::endl; 
      // etc 
     } 
     return EXIT_SUCCESS; 
    } 
    catch (std::exception const& e) 
    { 
     std::cerr << e.what() << std::endl; 
    } 
    return EXIT_FAILURE; 
} 

修改，你認爲合適。

打印整個樹來查看正在讀取的內容。這有助於調試。

void print(boost::property_tree::ptree const& pt) 
{ 
    using boost::property_tree::ptree; 
    ptree::const_iterator end = pt.end(); 
    for (ptree::const_iterator it = pt.begin(); it != end; ++it) { 
     std::cout << it->first << ": " << it->second.get_value<std::string>() << std::endl; 
     print(it->second); 
    } 
} 

Answer 3

只是糾正問題與上面的答案，但我不能得到正確格式化的評論：

#ifdef _MSC_VER 
#include <boost/config/compiler/visualc.hpp> 
#endif 
#include <boost/property_tree/ptree.hpp> 
#include <boost/property_tree/json_parser.hpp> 
#include <boost/foreach.hpp> 
#include <cassert> 
#include <exception> 
#include <iostream> 
#include <sstream> 
#include <string> 

void print(boost::property_tree::ptree const& pt) 
{ 
    using boost::property_tree::ptree; 
    ptree::const_iterator end = pt.end(); 
    for (ptree::const_iterator it = pt.begin(); it != end; ++it) { 
     std::cout << it->first << ": " << it->second.get_value<std::string>() << std::endl; 
     print(it->second); 
    } 
} 

int main() 
{ 
    try 
    { 
     std::stringstream ss; 
     // send your JSON above to the parser below, but populate ss first 

     ss << "{ \"particles\": [ { \"electron\": { \"pos\": [ 0, 0, 0 ], \"vel\": [ 0, 0, 0 ] }, \"proton\": { \"pos\": [ -1, 0, 0 ], \"vel\": [ 0, -0.1, -0.1 ] } } ]}"; 


     boost::property_tree::ptree pt; 
     boost::property_tree::read_json(ss, pt); 

     BOOST_FOREACH(boost::property_tree::ptree::value_type &v, pt.get_child("particles")) 
     { 
      assert(v.first.empty()); // array elements have no names 
      print(v.second); 
     } 
     return EXIT_SUCCESS; 
    } 
    catch (std::exception const& e) 
    { 
     std::cerr << e.what() << std::endl; 
    } 
    return EXIT_FAILURE; 
}