How to use vector::push_back()` with a struct?

问题:

How can I push_back a struct into a vector?

struct point {
    int x;
    int y;
};

std::vector<point> a;

a.push_back( ??? );

回答1:

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));

回答2:

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.

回答3:

struct point {
    int x;
    int y;
};

vector <point> a;

a.push_back( {6,7} );
a.push_back( {5,8} );

Use the curly bracket.

回答4:

point foo; //initialize with whatever
a.push_back(foo);