CODEWITHSUNDEEP
c++stlsgi
Joey.Z
Joey.Z

Reputation: 4770

A template function and a non-template overload of this function, which is a best match?

The code is as follows:

template <class InputIterator, class OutputIterator>
inline OutputIterator copy(InputIterator first, InputIterator last,
                           OutputIterator result)
{
  return __copy_dispatch<InputIterator,OutputIterator>()(first, last, result);
}

//A overload version
inline char* copy(const char* first, const char* last, char* result) {
  memmove(result, first, last - first);
  return result + (last - first);
}

If I call copy(int*, int*), which is the best match, will the compiler instantiate a new function use int* as the template parameter, or int* will be convert to char*.

And what if I call copy(char[], char[]) notice I just use char[] to note the type of parameters.

Upvotes: 2

Views: 446

Answers (2)

Ralph Tandetzky
Ralph Tandetzky

Reputation: 23610

Since int * is not implicitly convertible to char * nor to const char *, the template function will be called. Removing the template function would result in compile time error.

Suggestion: There is great value in playing around with the compiler yourself. You can add lines like 

std::cout << "template function called.\n";

into your overloads or use the debugger to do that kind of stuff. It's a great learning experience. You might also simply read some C++ books for an introduction.

Upvotes: 4

juanchopanza
juanchopanza

Reputation: 227418

if I call copy(int*, int*), which is the best match,

There in only one match: the template. The version taking const char* does not match at all.

And what if I call copy(char[], char[])

again, the template wins, because the arguments are not const. If you did this:

const char* c1 = ....;
const char* c2 = ....;
copy(c1, c2);

then the non-template would win, because in the case of a perfect overload match, a non-template function takes precedence.

Upvotes: 1

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