how can i sort my struct by x coordinate using std::sort

Question

here is my struct:

class Pont{

private:

    int x, y;
public:

    Pont( int x=0, int y=0);
    int getX() const;
    int getY() const;
    void setX( int x );
    void setY( int y );
    void move( int nx, int ny);
};

and I fill my Pont type pontok :

while(n < N){

        int x=(rand()%2000);
        int y=(rand()%2000);
        Pont p(x,y);
        if(!letezike(p,n)){
            pontok[n]=p;
            ++n;
        }

and I've tried with this:

bool sorter(Pont const& lhs, Pont const& rhs) {

   if (lhs.getX() != rhs.getX())
        return lhs.getX() < rhs.getX();
}

std::sort(pontok[0], pontok[N], &sorter);

Answer 1

Remove that != check. It gives your program undefined behaviour if the x values are equal because the function will not reach a return statement.

bool sorter(Pont const& lhs, Pont const& rhs) {
    return lhs.getX() < rhs.getX();
}

If the x values are equal, this will return false , as it should do.

Also, your call to std::sort is incorrect. Assuming pontok is an array of points of size N , you need to do:

std::sort(pontok, pontok + N, &sorter);

std::sort takes an iterator range which point to the beginning and end of the sequence you want to sort. You were passing in two elements of your array.

Answer 2

Your sorter function appears to return nothing when the X co-ordinates are equal, is that what you meant?!

It could be simply:

bool sorter(Pont const& lhs, Pont const& rhs) {
   return lhs.getX() < rhs.getX();
}