用boost讀取json文件

Question

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]
    }
}

如何通過解析此文件來創建粒子矢量。 據我所知，我需要使用boost讀取文件並將字符串（行）讀入向量，然后解析向量的內容。

類粒子是這樣的：

class Particle
{

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

在類中省略了get / set的其他方法。

基本上我想幫助創建一個vector<Particle>其中包含正確的位置和速度數據以及解析到其中的particle_type數據。 提前致謝。

代碼主要：

int main(){

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

Answer 1

我稍微修改了你的JSON。 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;
}

根據需要修改。

打印整個樹以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 2

您可以使用以下代碼進行迭代：

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.
}

希望能幫助到你

Answer 3

只是糾正上面的答案的問題，但我無法在評論中得到正確的格式化：

#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;
}