读取并解析 JSON 文件 c++ BOOST
Read & Parse a JSON file c++ BOOST
因为已经有很多关于这个的问题,我有点担心问...但是
我查看了许多不同的问题,但没有任何一个对我有用。我有此代码作为我的尝试,但它不起作用:
#include "boost/property_tree/ptree.hpp"
#include "boost/property_tree/json_parser.hpp"
using namespace boost::property_tree;
...
std::ifstream jsonFile("test_file.json");
if (!jsonFile){
std::cerr << "Error opening file\n";
return -1;
}
ptree pt;
json_parser::read_json(jsonFile, pt);
for (auto& array_element : pt) {
for (auto& property : array_element.second) {
std::cout << property.first << " = " << property.second.get_value<std::string>() << "\n";
}
}
其内容格式如下:
[{"number": 1234,"string": "hello world"}, {"number": 5678,"string": "foo bar"}, ... etc }]
我无法让它读出 1234
,然后再读出 hello world
。事实上,它什么都不做。如何从我的 .JSON
文件中读出?
我不完全确定问题出在哪里。它似乎有效(一旦你使 JSON 有效):
UPDATE: Boost JSON
Boost 1.75.0 introduced Boost JSON, far superior way to actually deal with Json: Live On Wandbox
#include <boost/json.hpp>
#include <boost/json/src.hpp>
#include <iostream>
#include <iterator>
#include <fstream>
namespace json = boost::json;
struct Rec {
int64_t number;
std::string string;
friend Rec tag_invoke(json::value_to_tag<Rec>, json::value const& v) {
auto& o = v.as_object();
return {
o.at("number").as_int64(),
value_to<std::string>(o.at("string")),
};
}
friend void tag_invoke(json::value_from_tag, json::value& v, Rec const& rec)
{
v = json::object{
{"number", rec.number},
{"string", rec.string},
};
}
};
int main() {
std::ifstream ifs("input.txt");
std::string input(std::istreambuf_iterator<char>(ifs), {});
using Recs = std::vector<Rec>;
Recs recs = value_to<std::vector<Rec>>(json::parse(input));
for (auto& [n, s] : recs) {
std::cout << "Rec { " << n << ", " << std::quoted(s) << " }\n";
// some frivolous changes:
n *= 2;
reverse(begin(s), end(s));
}
std::cout << "Modified json: " << json::value_from(recs) << "\n";
}
Printing
Rec { 1234, "hello world" }
Rec { 5678, "foo bar" }
Modified json: [{"number":2468,"string":"dlrow olleh"},{"number":11356,"string":"rab oof"}]
#include "boost/property_tree/ptree.hpp"
#include "boost/property_tree/json_parser.hpp"
int main() {
using boost::property_tree::ptree;
std::ifstream jsonFile("input.txt");
ptree pt;
read_json(jsonFile, pt);
for (auto & array_element: pt) {
for (auto & property: array_element.second) {
std::cout << property.first << " = " << property.second.get_value < std::string > () << "\n";
}
}
}
与input.txt
包含:
[{"number": 1234, "string": "hello world"},{"number": 5678, "string": "foo bar"}]
版画
number = 1234
string = hello world
number = 5678
string = foo bar
因为已经有很多关于这个的问题,我有点担心问...但是
我查看了许多不同的问题,但没有任何一个对我有用。我有此代码作为我的尝试,但它不起作用:
#include "boost/property_tree/ptree.hpp"
#include "boost/property_tree/json_parser.hpp"
using namespace boost::property_tree;
...
std::ifstream jsonFile("test_file.json");
if (!jsonFile){
std::cerr << "Error opening file\n";
return -1;
}
ptree pt;
json_parser::read_json(jsonFile, pt);
for (auto& array_element : pt) {
for (auto& property : array_element.second) {
std::cout << property.first << " = " << property.second.get_value<std::string>() << "\n";
}
}
其内容格式如下:
[{"number": 1234,"string": "hello world"}, {"number": 5678,"string": "foo bar"}, ... etc }]
我无法让它读出 1234
,然后再读出 hello world
。事实上,它什么都不做。如何从我的 .JSON
文件中读出?
我不完全确定问题出在哪里。它似乎有效(一旦你使 JSON 有效):
UPDATE: Boost JSON
Boost 1.75.0 introduced Boost JSON, far superior way to actually deal with Json: Live On Wandbox
#include <boost/json.hpp> #include <boost/json/src.hpp> #include <iostream> #include <iterator> #include <fstream> namespace json = boost::json; struct Rec { int64_t number; std::string string; friend Rec tag_invoke(json::value_to_tag<Rec>, json::value const& v) { auto& o = v.as_object(); return { o.at("number").as_int64(), value_to<std::string>(o.at("string")), }; } friend void tag_invoke(json::value_from_tag, json::value& v, Rec const& rec) { v = json::object{ {"number", rec.number}, {"string", rec.string}, }; } }; int main() { std::ifstream ifs("input.txt"); std::string input(std::istreambuf_iterator<char>(ifs), {}); using Recs = std::vector<Rec>; Recs recs = value_to<std::vector<Rec>>(json::parse(input)); for (auto& [n, s] : recs) { std::cout << "Rec { " << n << ", " << std::quoted(s) << " }\n"; // some frivolous changes: n *= 2; reverse(begin(s), end(s)); } std::cout << "Modified json: " << json::value_from(recs) << "\n"; }
Printing
Rec { 1234, "hello world" } Rec { 5678, "foo bar" } Modified json: [{"number":2468,"string":"dlrow olleh"},{"number":11356,"string":"rab oof"}]
#include "boost/property_tree/ptree.hpp"
#include "boost/property_tree/json_parser.hpp"
int main() {
using boost::property_tree::ptree;
std::ifstream jsonFile("input.txt");
ptree pt;
read_json(jsonFile, pt);
for (auto & array_element: pt) {
for (auto & property: array_element.second) {
std::cout << property.first << " = " << property.second.get_value < std::string > () << "\n";
}
}
}
与input.txt
包含:
[{"number": 1234, "string": "hello world"},{"number": 5678, "string": "foo bar"}]
版画
number = 1234
string = hello world
number = 5678
string = foo bar