More specific overload not called

Question

Given the following two functions, I would expect the first overload to be called if I pass it an std::pair<const char*, std::size_t>, since it is more specific than a generic T.

void foo(const std::pair<const char*, std::size_t>& p)
{
    std::cout << "pair" << std::endl;
}

template <class T>
void foo(const T& v)
{
    std::cout << "generic" << std::endl;
}

int main()
{
    const char* s = "abc";
    foo(std::make_pair(s, std::size_t(3)));
}

However, this program outputs:

generic

Why is the second overload called, instead of the overload that explicitly takes a pair?

Is this a compiler issue? I happen to be using a pretty old compiler (GCC 4.1.2) at the moment.

Hmm... it probably IS a compiler issue:

http://ideone.com/97XwwZ

Answer 1

Your compiler is certainly in error. What error it is, will only be speculation, but you are correct that this code should give the more specific output. The sample isn't big or complex enough for any of the more subtle rules to be the cause.