c++, JSON, get object members in an array
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I am using nlohmann::json for parsing json in the program.
given a json there is an array with several objects, according to one of the object members I want to get other members of the same object.
like in the json below
{
"arr":[
{"a":1, "b":11, "c":111, ...},
{"a":2, "b":22, "c":222, ...},
{"a":3, "b":33, "c":333, ...},
...
]
}
for instance if the value of a is 2, I want to get the values of b,c,... of the same index/object.
currently I am using a for loop and at the index that j["arr"][i]["a"].get<int> == 2 going for the rest of members. As the array might have hundreds of members it is nonsense.
what is the best approach in this case?
c++ json nlohmann-json
asked Nov 16 '18 at 16:36
Amir-MousaviAmir-Mousavi
86111238
add a comment |
I am using nlohmann::json for parsing json in the program.
given a json there is an array with several objects, according to one of the object members I want to get other members of the same object.
like in the json below
{
"arr":[
{"a":1, "b":11, "c":111, ...},
{"a":2, "b":22, "c":222, ...},
{"a":3, "b":33, "c":333, ...},
...
]
}
for instance if the value of a is 2, I want to get the values of b,c,... of the same index/object.
currently I am using a for loop and at the index that j["arr"][i]["a"].get<int> == 2 going for the rest of members. As the array might have hundreds of members it is nonsense.
what is the best approach in this case?
c++ json nlohmann-json
asked Nov 16 '18 at 16:36
Amir-MousaviAmir-Mousavi
86111238
add a comment |
I am using nlohmann::json for parsing json in the program.
given a json there is an array with several objects, according to one of the object members I want to get other members of the same object.
like in the json below
{
"arr":[
{"a":1, "b":11, "c":111, ...},
{"a":2, "b":22, "c":222, ...},
{"a":3, "b":33, "c":333, ...},
...
]
}
for instance if the value of a is 2, I want to get the values of b,c,... of the same index/object.
currently I am using a for loop and at the index that j["arr"][i]["a"].get<int> == 2 going for the rest of members. As the array might have hundreds of members it is nonsense.
what is the best approach in this case?
c++ json nlohmann-json
asked Nov 16 '18 at 16:36
Amir-MousaviAmir-Mousavi
86111238
I am using nlohmann::json for parsing json in the program.
given a json there is an array with several objects, according to one of the object members I want to get other members of the same object.
like in the json below
{
"arr":[
{"a":1, "b":11, "c":111, ...},
{"a":2, "b":22, "c":222, ...},
{"a":3, "b":33, "c":333, ...},
...
]
}
for instance if the value of a is 2, I want to get the values of b,c,... of the same index/object.
currently I am using a for loop and at the index that j["arr"][i]["a"].get<int> == 2 going for the rest of members. As the array might have hundreds of members it is nonsense.
what is the best approach in this case?
c++ json nlohmann-json
c++ json nlohmann-json
asked Nov 16 '18 at 16:36
Amir-MousaviAmir-Mousavi
86111238
asked Nov 16 '18 at 16:36
Amir-MousaviAmir-Mousavi
86111238
asked Nov 16 '18 at 16:36
Amir-MousaviAmir-Mousavi
86111238
asked Nov 16 '18 at 16:36
Amir-MousaviAmir-Mousavi
86111238
asked Nov 16 '18 at 16:36
Amir-MousaviAmir-Mousavi
86111238
86111238
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
It's a JSON array, you need to iterate over it. So your approach is the simple and direct one.
answered Nov 19 '18 at 9:35
riokirioki
4,16442448
add a comment |
Let's call the C++ type of the elements of arr Thing, you can convert arr to a std::vector<Thing>.
void to_json(nlohmann::json & j, const Thing & t) {
j = nlohmann::json{{"a", t.a}, {"b", t.b}, {"c", t.c}}; // similarly other members ...
}
void from_json(const nlohmann::json & j, Thing & t) {
j.at("a").get_to(t.a);
j.at("b").get_to(t.b);
j.at("c").get_to(t.c); // similarly other members ...
}
std::vector<Thing> things = j["arr"];
auto it = std::find_if(things.begin(), things.end(), (const Thing & t){ return t.a ==2; });
// use it->b etc
answered Nov 19 '18 at 10:16
CalethCaleth
18.8k22142
add a comment |
x2struct(https://github.com/xyz347/x2struct) can load json to struct with condition.
#include "x2struct.hpp"
#include <iostream>
using namespace std;
struct Item {
int a;
int b;
int c;
XTOSTRUCT(O(a,b,c));
XTOSTRUCT_CONDITION() { // load only this return true
int a = -1;
if (obj.has("a")) {
obj["a"].convert(a);
}
return a==2;
}
};
struct Test {
Item arr;
XTOSTRUCT(O(arr));
};
int main(int argc, char *argv) {
string jstr = "{"arr":[{"a":1, "b":11, "c":111},{"a":2, "b":22, "c":222},{"a":3, "b":33, "c":333}]}";
Test t;
x2struct::X::loadjson(jstr, t, false);
cout<<t.arr.b<<','<<t.arr.c<<endl;
}
output is:
22,222
answered Nov 19 '18 at 9:27
xyz347xyz347
613
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
It's a JSON array, you need to iterate over it. So your approach is the simple and direct one.
answered Nov 19 '18 at 9:35
riokirioki
4,16442448
add a comment |
It's a JSON array, you need to iterate over it. So your approach is the simple and direct one.
answered Nov 19 '18 at 9:35
riokirioki
4,16442448
add a comment |
It's a JSON array, you need to iterate over it. So your approach is the simple and direct one.
answered Nov 19 '18 at 9:35
riokirioki
4,16442448
It's a JSON array, you need to iterate over it. So your approach is the simple and direct one.
answered Nov 19 '18 at 9:35
riokirioki
4,16442448
answered Nov 19 '18 at 9:35
riokirioki
4,16442448
answered Nov 19 '18 at 9:35
riokirioki
4,16442448
answered Nov 19 '18 at 9:35
riokirioki
4,16442448
4,16442448
add a comment |
add a comment |
Let's call the C++ type of the elements of arr Thing, you can convert arr to a std::vector<Thing>.
void to_json(nlohmann::json & j, const Thing & t) {
j = nlohmann::json{{"a", t.a}, {"b", t.b}, {"c", t.c}}; // similarly other members ...
}
void from_json(const nlohmann::json & j, Thing & t) {
j.at("a").get_to(t.a);
j.at("b").get_to(t.b);
j.at("c").get_to(t.c); // similarly other members ...
}
std::vector<Thing> things = j["arr"];
auto it = std::find_if(things.begin(), things.end(), (const Thing & t){ return t.a ==2; });
// use it->b etc
answered Nov 19 '18 at 10:16
CalethCaleth
18.8k22142
add a comment |
Let's call the C++ type of the elements of arr Thing, you can convert arr to a std::vector<Thing>.
void to_json(nlohmann::json & j, const Thing & t) {
j = nlohmann::json{{"a", t.a}, {"b", t.b}, {"c", t.c}}; // similarly other members ...
}
void from_json(const nlohmann::json & j, Thing & t) {
j.at("a").get_to(t.a);
j.at("b").get_to(t.b);
j.at("c").get_to(t.c); // similarly other members ...
}
std::vector<Thing> things = j["arr"];
auto it = std::find_if(things.begin(), things.end(), (const Thing & t){ return t.a ==2; });
// use it->b etc
answered Nov 19 '18 at 10:16
CalethCaleth
18.8k22142
add a comment |
Let's call the C++ type of the elements of arr Thing, you can convert arr to a std::vector<Thing>.
void to_json(nlohmann::json & j, const Thing & t) {
j = nlohmann::json{{"a", t.a}, {"b", t.b}, {"c", t.c}}; // similarly other members ...
}
void from_json(const nlohmann::json & j, Thing & t) {
j.at("a").get_to(t.a);
j.at("b").get_to(t.b);
j.at("c").get_to(t.c); // similarly other members ...
}
std::vector<Thing> things = j["arr"];
auto it = std::find_if(things.begin(), things.end(), (const Thing & t){ return t.a ==2; });
// use it->b etc
answered Nov 19 '18 at 10:16
CalethCaleth
18.8k22142
Let's call the C++ type of the elements of arr Thing, you can convert arr to a std::vector<Thing>.
void to_json(nlohmann::json & j, const Thing & t) {
j = nlohmann::json{{"a", t.a}, {"b", t.b}, {"c", t.c}}; // similarly other members ...
}
void from_json(const nlohmann::json & j, Thing & t) {
j.at("a").get_to(t.a);
j.at("b").get_to(t.b);
j.at("c").get_to(t.c); // similarly other members ...
}
std::vector<Thing> things = j["arr"];
auto it = std::find_if(things.begin(), things.end(), (const Thing & t){ return t.a ==2; });
// use it->b etc
answered Nov 19 '18 at 10:16
CalethCaleth
18.8k22142
answered Nov 19 '18 at 10:16
CalethCaleth
18.8k22142
answered Nov 19 '18 at 10:16
CalethCaleth
18.8k22142
answered Nov 19 '18 at 10:16
CalethCaleth
18.8k22142
18.8k22142
add a comment |
add a comment |
x2struct(https://github.com/xyz347/x2struct) can load json to struct with condition.
#include "x2struct.hpp"
#include <iostream>
using namespace std;
struct Item {
int a;
int b;
int c;
XTOSTRUCT(O(a,b,c));
XTOSTRUCT_CONDITION() { // load only this return true
int a = -1;
if (obj.has("a")) {
obj["a"].convert(a);
}
return a==2;
}
};
struct Test {
Item arr;
XTOSTRUCT(O(arr));
};
int main(int argc, char *argv) {
string jstr = "{"arr":[{"a":1, "b":11, "c":111},{"a":2, "b":22, "c":222},{"a":3, "b":33, "c":333}]}";
Test t;
x2struct::X::loadjson(jstr, t, false);
cout<<t.arr.b<<','<<t.arr.c<<endl;
}
output is:
22,222
answered Nov 19 '18 at 9:27
xyz347xyz347
613
add a comment |
x2struct(https://github.com/xyz347/x2struct) can load json to struct with condition.
#include "x2struct.hpp"
#include <iostream>
using namespace std;
struct Item {
int a;
int b;
int c;
XTOSTRUCT(O(a,b,c));
XTOSTRUCT_CONDITION() { // load only this return true
int a = -1;
if (obj.has("a")) {
obj["a"].convert(a);
}
return a==2;
}
};
struct Test {
Item arr;
XTOSTRUCT(O(arr));
};
int main(int argc, char *argv) {
string jstr = "{"arr":[{"a":1, "b":11, "c":111},{"a":2, "b":22, "c":222},{"a":3, "b":33, "c":333}]}";
Test t;
x2struct::X::loadjson(jstr, t, false);
cout<<t.arr.b<<','<<t.arr.c<<endl;
}
output is:
22,222
answered Nov 19 '18 at 9:27
xyz347xyz347
613
add a comment |
x2struct(https://github.com/xyz347/x2struct) can load json to struct with condition.
#include "x2struct.hpp"
#include <iostream>
using namespace std;
struct Item {
int a;
int b;
int c;
XTOSTRUCT(O(a,b,c));
XTOSTRUCT_CONDITION() { // load only this return true
int a = -1;
if (obj.has("a")) {
obj["a"].convert(a);
}
return a==2;
}
};
struct Test {
Item arr;
XTOSTRUCT(O(arr));
};
int main(int argc, char *argv) {
string jstr = "{"arr":[{"a":1, "b":11, "c":111},{"a":2, "b":22, "c":222},{"a":3, "b":33, "c":333}]}";
Test t;
x2struct::X::loadjson(jstr, t, false);
cout<<t.arr.b<<','<<t.arr.c<<endl;
}
output is:
22,222
answered Nov 19 '18 at 9:27
xyz347xyz347
613
x2struct(https://github.com/xyz347/x2struct) can load json to struct with condition.
#include "x2struct.hpp"
#include <iostream>
using namespace std;
struct Item {
int a;
int b;
int c;
XTOSTRUCT(O(a,b,c));
XTOSTRUCT_CONDITION() { // load only this return true
int a = -1;
if (obj.has("a")) {
obj["a"].convert(a);
}
return a==2;
}
};
struct Test {
Item arr;
XTOSTRUCT(O(arr));
};
int main(int argc, char *argv) {
string jstr = "{"arr":[{"a":1, "b":11, "c":111},{"a":2, "b":22, "c":222},{"a":3, "b":33, "c":333}]}";
Test t;
x2struct::X::loadjson(jstr, t, false);
cout<<t.arr.b<<','<<t.arr.c<<endl;
}
output is:
22,222
answered Nov 19 '18 at 9:27
xyz347xyz347
613
answered Nov 19 '18 at 9:27
xyz347xyz347
613
answered Nov 19 '18 at 9:27
xyz347xyz347
613
answered Nov 19 '18 at 9:27
xyz347xyz347
613
613
add a comment |
add a comment |
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