How can I push_back a struct into a vector?
struct point {
int x;
int y;
};
std::vector<point> a;
a.push_back( ??? );
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5 Answers
point mypoint = {0, 1};
a.push_back(mypoint);
Or if you're allowed, give point a constructor, so that you can use a temporary:
a.push_back(point(0,1));
Some people will object if you put a constructor in a class declared with struct, and it makes it non-POD, and maybe you aren't in control of the definition of point. So this option might not be available to you. However, you can write a function which provides the same convenience:
point make_point(int x, int y) {
point mypoint = {x, y};
return mypoint;
}
a.push_back(make_point(0, 1));
answered Mar 13, 2011 at 13:23
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3how does make_point function work, will the local var mypoint be not out of scope after the return?– user1065101Commented Mar 27, 2016 at 7:58
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1
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3@ThePunisher: definitely, but the question was asked 7 years ago about
push_back, so I wasn't going to give a non-standard answer that the questioner's implementation may or may not have implemented yet :-) Commented Apr 13, 2018 at 11:32 -
1If you have a constructor you should probably use
emplace_back()instead ofpush_back(). Commented May 15, 2018 at 12:55
point p;
p.x = 1;
p.y = 2;
a.push_back(p);
Note that, since a is a vector of points (not pointers to them), the push_back will create a copy of your point struct -- so p can safely be destroyed once it goes out of scope.
struct point {
int x;
int y;
};
vector <point> a;
a.push_back( {6,7} );
a.push_back( {5,8} );
Use the curly bracket.
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This is nice, but how does emplace_back() compares to this, is it better in some way?– bbvCommented Apr 10, 2019 at 7:04
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@bbv You need a constructor for emplace_back(). Doing it like Rewd0n should however invoke the move variant of push_back, so the end result is pretty much the same.– marcbfCommented Mar 3, 2020 at 6:36
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point foo; //initialize with whatever
a.push_back(foo);
answered Mar 13, 2011 at 13:22
We should use emplace_back() for user defined data types such as structs.We can use it even with primitive data types as well.
