C++ 使用boost读取json文件
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Reading json file with boost
提问by user3728501
I have a file like this:
我有一个这样的文件：
[data.json]
[数据.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]
}
}
How do I create a vector of particles from parsing this file. As I understand it I need to read the file using boost and read the strings (lines) into a vector, and then parse the contents of the vector.
如何通过解析此文件创建粒子向量。据我了解，我需要使用 boost 读取文件并将字符串（行）读入向量，然后解析向量的内容。
The class particle is something like this:
类粒子是这样的：
class Particle
{
private:
particle_type mtype; // particle_type is an enum
vector<double> mPos;
vector<double> mVel;
};
Other methods for get/set have been omitted in the class.
类中省略了其他 get/set 方法。
Basically I would like help creating a vector<Particle>with the correct position and velocity data and particle_type data parsed into it. Thanks in advance.
基本上我想帮助创建一个vector<Particle>具有正确位置和速度数据以及解析到其中的particle_type数据。提前致谢。
Code in main:
主要代码：
int main(){
boost::property_tree::ptree pt;
boost::property_tree::read_json("data.json", pt);
}
回答by
I modified your JSON a bit. Slightly untested code.
我稍微修改了你的 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;
}
Modify as you see fit.
根据您的需要进行修改。
Print the entire tree to see what is being read. This helps in debugging.
打印整个树以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);
}
}
回答by Y__
You can iterate with the following code :
您可以使用以下代码进行迭代：
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.
}
Hope it helps
希望能帮助到你
回答by Jim
Just correcting issues with the answer above but I couldnt get the formating correct in the comments:
只是用上面的答案纠正问题，但我无法在评论中获得正确的格式：
#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;
}
