Why do two functions have the same address?

Question

Consider this function template:

template
unsigned long f(void *) { return 0;}

Now, I print the addresses of f

Answer 1

This is simply a case of undefined behavior because the results of casting a pointer to a function to a pointer to object type are undefined.

A more interesting expression to examine would bef<A> == f<B> which should evaluate to true if and only if A and B refer to the same type.

Answer 2

You need to cast to void *:

std::cout << (void*)(ftype*)f<A> << std::endl;
std::cout << (void*)(ftype*)f<B> << std::endl;

If you cast to a function pointer (or several other classes of non-void pointers), it will be interpreted as a bool by the operator<< for std::ostream (hence the 1).

Answer 3

Since the function doesn't depend on the template parameter, the compiler can condense all instantiations into a single function.

I don't know why you get 1 for the address.

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Added by Nawaz:

I experimented with my real code, and concluded that what @Mark said above is very important here :

Since the function doesn't depend on the template parameter, the compiler can condense all instantiations into a single function.

I also came to a conclusion that if the function-body depends on T*, not on T, it still produces the same function for different type arguments in my real code (not on ideone, though). However, if it depends on T, then it produces different functions, because sizeof(T) differs (fortunately for me) for different type arguments.

So I added a dummy automatic variable of type T in the function template, so that the function could depend on the size of T so as to force it to produce different functions.