如何用Boost读取json文件?

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我有这样一个文件:

[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]
    }
}

如何从解析此文件创建粒子矢量。据我了解,我需要使用boost来读取文件,并将字符串(行)读入向量,然后解析向量的内容。

类粒子是这样的:

class Particle
{

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

其他获取/设置方法在课程中已被省略。

基本上我想帮助创建一个vector<Particle>正确的位置和速度数据和particle_type数据解析到它。提前致谢。

主要代码:

int main(){

    boost::property_tree::ptree pt;
    boost::property_tree::read_json("data.json", pt);
}
提问于
用户回答回答于

你可以迭代下面的代码:

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.
}
用户回答回答于

我修改了一下你的JSON。稍微未经测试的代码。

{
    "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;
}

根据你的看法修改。

打印整个树来查看正在读取的内容。这有助于调试。

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);
    }
}

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