C ++模板类编译错误

Question

I get the following compilation error:

main.cc: In function 'int main(int, char**)':¶
main.cc:200: error: no match for 'operator==' in 'rt1 == rt2'¶
triple.hh:124: note: candidates are: bool Triple<T1, T2, T3>::operator==(const    Triple<T1,T2, T3>&) [with T1 = int, T2 = int, T3 = int] <near match>¶
main.cc:27: note:                 bool operator==(const Special&, const Special&)¶

Although I have implemented the operator== overload as follows for my template class:

bool operator==(const Triple<T1, T2, T3>& another) {
    return (a == another.first() and b == another.second() and c == another.third());
}

For my template class:

template <typename T1, typename T2, typename T3>
class Triple

Do you know what the problem might be? Many thanks.

Answer 1

Your boolean operator is declared as non-const. Fix it as follows in case rt1 is a const reference. Note the added const keyword.

bool operator==(const Triple<T1, T2, T3>& another) const {

Explanation: C++ has two basic syntaxes for overloading a comparison operator; a member operator with one other argument, or a static operator with two arguments. However, in both cases, you should make sure that both operands are const , with the respective syntaxes.

It is theoretically possible to supply different const and non- const versions of the operator that do subtly different things, so the compiler calls yours a near-match, but nevertheless not a match.