Question

template<int* A,int* B>
void f()
{
}
template<int A,int B>
void f()
{
}
void main()
{
    f<(int*)1,(int*)2>();
}

I’d like have two specializtions of my template finction f. But this code isn’t compiled. What’s the problem?

Error   1   error C2440: "specialization" : cannot convert from "int *" to "const int" line 11
Error   2   error C2973: invalid template argument "int *" line 11
Error   3   error C2440: "specialization" : cannot convert from "int *" to "const int" line 11
Error   4   error C2973: invalid template argument "int *" line 11
Error   5   error C2668: 'f' : ambiguous call to overloaded function line 11

Compiler Visual C++ 2010

Answer 1

You are trying to use an address as template parameter. If you try to compile the code with gcc or clang, you get, in gcc

test.cpp:11:13: error: a cast to a type other than an integral or enumeration type cannot     appear in a constant-expression
test.cpp:11:21: error: a cast to a type other than an integral or enumeration type cannot appear in a constant-expression

and in clang:

candidate template ignored: invalid explicitly-specified argument for template parameter 'A'

which is correct, according to this answer: Casting pointer as template argument: Comeau & MSVC compile, GCC fails

That is, although pointers are accepted, they should only be pointers to named objects with external linkage.