C++ error: map.insert(make_pair(struct, vector));

Question

The following code that is a part of a chess game im making where the key are the position of the piece and the value is the possible moves that piece have

#include<iostream>
#include<map>
#include<vector>

using namespace std;

struct Coordinate{
    int x, y;
};

int main(){
    map<Coordinate, vector<Coordinate>> moves;//map that have an struct as key and a vector of structs as value.
    //There is the error
    moves.insert(make_pair(Coordinate{0,0},//the struct
                               vector<Coordinate>{Coordinate{1,1},//the vector
                                                  Coordinate{2,2},
                                                  Coordinate{3,3}}));
    return 0;
};

Thos code gets me to the line 235 in file 'stl_function.h'

Where's the `>`? You'll also need a custom comparator or `operator<` on `Coordinate`. — LogicStuff, Mar 28 '16 at 20:47
I do not get any error in my source code, Code::Blocks get me to the file 'stl_function.h' and there says: `In instantation of 'bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = Coordinate]' — Roberto Jaimes, Mar 28 '16 at 20:54
@Roberto `std::map` is sorted by keys, you need to provide one of the aforementioned functions. — LogicStuff, Mar 28 '16 at 20:56
i fixed the `>` missed, an error i have made when copying the code, but the error of the cuestion continues. — Roberto Jaimes, Mar 28 '16 at 20:57
FYI: `movements.insert({{0,0}, {{1,1}, {2,2}, {3,3}}});` also works. — David, Mar 28 '16 at 21:02

score 4 · Accepted Answer · answered Mar 28 '16 at 20:57

4

You need to provide a custom comparator to your struct:

struct Coordinate{
    int x, y;

    constexpr bool operator<(const Coordinate & rhs) const
    {
        return x < rhs.x && y < rhs.y;   
    }
};

answered Mar 28 '16 at 20:57

hlscalon

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Tanks that solved my problem. i am a starter with c++, can you tell me what is `rhs`? – Roberto Jaimes Mar 28 '16 at 21:03
1

@RobertoJaimes it stands for 'right hand side', cuz it's used for the right hand side of the `<` comparison. It's common to name that argument "rhs" or "other" – David Mar 28 '16 at 21:05

C++ error: map.insert(make_pair(struct, vector));

1 Answers1