Overloaded Templates and Conversions

There’s one case we haven’t covered so far: pointers to C-style character strings and string literals. Now that we have a version of debug_rep that takes a string, we might expect that a call that passes character strings would match that version. However, consider this call:

cout << debug_rep("hi world!") << endl; // calls debug_rep(T*)

Here all three of the debug_rep functions are viable:

• debug_rep(const T&), with T bound to char[10]

• debug_rep(T*), with T bound to const char

• debug_rep(const string&), which requires a conversion from const char* to string

Both templates provide an exact match to the argument—the second template requires a (permissible) conversion from array to pointer, and that conversion is considered as an exact match for function-matching purposes (§ 6.6.1, p. 245). The nontemplate version is viable but requires a user-defined conversion. That function is less good than an exact match, leaving the two templates as the possible functions to call. As before, the T* version is more specialized and is the one that will be selected.

If we want to handle character pointers as strings, we can define two more nontemplate overloads:

// convert the character pointers to string and call the string version of debug_rep
string debug_rep(char *p)
{
    return debug_rep(string(p));
}
string debug_rep(const char *p)
{
    return debug_rep(string(p));
}