Why am I getting ambiguous call for the following functions?

Consider the following:

template <typename T>
class testString
{
publi开发者_如何转开发c:

  typedef T* iterator;

  void insert(iterator aPos, size_t numChars, T aChar);
  testString<T>& insert(size_t aIndex, size_t numChars, T aChar);
};

template <typename T>
void testString<T>::insert( iterator aPos, size_t numChars, T aChar )
{

}

template <typename T>
testString<T>& testString<T>::insert( size_t aIndex, size_t numChars, T aChar )
{
  return *this;
}

int main()
{
  testString<char> c;
  c.insert(0, 10, 'a'); // ambiguous call
  c.insert(1, 10, 'a'); // compiles fine

  return 0;
}

Why am I getting an ambiguous call? Initially, I had a guess (because it is 0, it can be anything), but then I looked at std::string. I looked at the source, and these are the two functions:

void               insert ( iterator p, size_t n, char c );
string&            insert ( size_t pos1, size_t n, char c );

And I tried the same calls with std::string, and it works fine. Now I have no clue why 0 works with std::string and is immediately recognized as a size_t while in my implementation it is not (another guess was type traits, but there is no evidence of it in the source)?

Ah, one of those times when you're like "wouldn't it be better if in c++, 0 was not the same as null?"

Anyway, your iterator type is typedef'd to T*, which is char*, and 0 is a fine value for a char*, hence the ambiguity (er, as K-ballo wrote). In std::string, the iterator type won't be a char*, it'll be something fancy like another (templatized) class...

Since 0 could be treated both as a pointer and an integer, you get the ambiguity.

If you want to distinguish them, my suggestion would be to wrap your T * in a class inside testClass. That is something like:

template <typename T>
class testString
{
public:
  class iterator
  {
  public:
    T *addr;
  }
  void insert(iterator aPos, size_t numChars, T aChar);
  testString<T>& insert(size_t aIndex, size_t numChars, T aChar);
};

If you have noticed, to STL either, you can't send an integer value as iterator, but you must pass an iterator of type whateverclass<whatevertype>::iterator.