Some const char * are unavailable at compile time?

Question

Let\'s suppose we have a template function with non-type parameter of const char * like this:

template  void print()         


        

Answer 1

The instantiation variable of a template needed to have external linkage, and const was implicitly internal linkage. So you have to write:

extern char const constMessage[] = "Const message";

(Another alternative would be for it to be a static class member. Static class members always have external linkage.)

The case of string literals is in some ways similar: their type is char const[]. But it's even worse: template instantiations (at least the early ones) need a name, and a string literal doesn't have one. Even more to the point, it's unspecified whether identical string literals are the same object or not, so in the following:

template 
struct Toto { char const* f() const; };

Toto <"titi"> t1;
Toto <"titi"> t2;

it would be unspecified whether t1 and t2 had the same type or not.