trouble inserting a struct into a set C++

问题

I am working on an A* pathfinding algorithm, but am having trouble with an error I receive when i insert a struct called node into a set. The error reads: "Error 1 error C2678: binary '<' : no operator found which takes a left-hand operand of type 'const node' (or there is no acceptable conversion)" but the error is found in another file 'XSTDDEF' which i haven't looked at. I am unsure of what it means.

struct node{
    int f;
    int g;
    int h;
    int x;
    int y;
};

node coords[24] = { -1 };

std::set<node> open;
std::set<node> closed;

int main(int argc, char *argv[]){
    coords[4].g = 0;
    coords[4].h = heuristic(start, end, start.h);
    coords[4].f = start.g + start.h;
    coords[4].x = 4;
    coords[4].y = 0;

    open.insert(coords[4]);

回答1:

As you may know if you've familiarized yourself with the documentation of std::set, it is an ordered container. Therefore there must be a way to compare the elements of the set so that they can be ordered. From the documentation, we know that the default comparison functor of std::set is std::less<T>.

Further, as you may know, std::less<T> does:

Unless specialized, invokes operator< on type T.

Since std::less isn't specialized for node, it uses operator<.

The error message tells you that an overload for operator< does not exist that would have const node (or anything that a node could be converted to) as the left operand.

The solution is to define such overload.

回答2:

std::set is an ordered container so it needs operator< to compare and order elements, allowing fast search. If you don't need this you can use list or vector.

回答3:

You need to create operator<or specialize std::less for your struct. Another solution could be to use std::array:

struct node : std::array<5,int> {
    int &f() { return data()[0]; }
    int &g() { return data()[1]; }
    int &h() { return data()[2]; }
    int &x() { return data()[3]; }
    int &y() { return data()[4]; }
};

and you will inherit operator< from it. Another benefit - you can access underlying data as array, which would simplify serializing etc.

来源：https://stackoverflow.com/questions/40914705/trouble-inserting-a-struct-into-a-set-c

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c++

struct

set

nodes