CODEWITHSUNDEEP
c++templatesoperator-overloading
SnowFatal
SnowFatal

Reputation: 2431

C++: template class with comparison operator overloading

I have a template class with three template types (basically a pair with one more member) and I can't get the comparison overload to work:

header:

template<typename FirstType, typename SecondType, typename ThirdType>
class Triple
{
public:
    Triple(FirstType f, SecondType s, ThirdType t) : var1(f), var2(s), var3(t)
    {}
...
private:
    FirstType var1;
    SecondType var2;
    ThirdType var3;
};


template<typename F1, typename S1, typename T1, typename F2, typename S2, typename T2>
bool operator==(const Triple<F1,S1,T1>& one, const Triple<F2,S2,T2>& other)
{
    return true; //just for testing
}


template<typename F1, typename S1, typename T1, typename F2, typename S2, typename T2>
bool testFunc(const Triple<F1,S1,T1>& one, const Triple<F2,S2,T2>& other)
{
    return true; //just for testing
}

main:

Triple<int, int, int> asdf(1, 1, 2);
Triple<int, int, int> qwer(1, 21, 2);
cout << asfd == qwer;         //doesn't work
cout << testFunc(asfd, qwer); //works

I get the following error message with the == operator:

binary '==' : no operator found which takes a right-hand operand of type 'Triple<FirstType,SecondType,ThirdType>'

Why testFunc works but the operator overload doesn't? Note that I want to include the possibility of comparing two different types of Triples, since someone might want to compare ints with doubles, for instance. I also tried implementing the comparison function inside the class with same results.

Upvotes: 1

Views: 2604

Answers (1)

SirGuy
SirGuy

Reputation: 10770

<< has a higher precedence than ==. This means your expression is parsed as

    (cout << asdf) == qwer;

Just add brackets to fix this

   cout << (asdf == qwer);

Upvotes: 5

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