Question

I’m getting a weird compiler error and as I’m new to using set’s with custom struct’s I’m not sure what exactly the problem is.

I’m trying to create a set of “pair’s” and am using a custom comparison function for inserting said pair’s.

struct pairT {
    std::string first, second;
};

int PairCmp(pairT &one, pairT &two) {
    if (one.first < two.first && one.second == two.second) return 0;
    else if (one.first < two.first) return -1;
    else if (one.first == two.first && one.second < two.second) return -1;
    return 1;
}

std::set<pairT> CartesianProduct (std::set<std::string> &one, std::set<std::string> &two) {
    std::set<pairT> returnSet(PairCmp);
    /.../

I’m getting the error from the last line of code:
C2664 “can’t convert parameter 1 from int to const std::less… blah, blah, blah.

Any suggestions as to why I’m getting my ass kicked?

Answer 1

Using objects (instead of pointers) requires that you name a second template parameter for std::set used to compare two objects of pairT. See std::less<> for an example.

Also, what you’re trying here seems to be wrong. You’re trying to return a std::set in CartesianProduct(), but the returned PairCmp() returns an integer.