_>// header.h
_>template<class T> void f(T);

_>//template<> void f(int);

_>inline void fi(int x) { f(x); }
_>

_>#include "header.h"

_>template<> void f(int x) {}
_>

If a template, a member template or a member of a class template is explicitly specialized then that specialization shall be declared before the first use of that specialization that would cause an implicit instantiation to take place, in every translation unit in which such a use occurs; no diagnostic is required. If the program does not provide a definition for an explicit specialization and either the specialization is used in a way that would cause an implicit instantiation to take place or the member is a virtual member function, the program is ill-formed, no diagnostic required. An implicit instantiation is never generated for an explicit specialization that is declared but not defined.

_>// header.h
_>template<class T> void f(T);

_>//template<> void f(int);

_>inline void fi(int x) { f(x); }
_>

_>#include "header.h"

_>template<> void f(int x) {}
_>

If a template, a member template or a member of a class template is explicitly specialized then that specialization shall be declared before the first use of that specialization that would cause an implicit instantiation to take place, in every translation unit in which such a use occurs; no diagnostic is required. If the program does not provide a definition for an explicit specialization and either the specialization is used in a way that would cause an implicit instantiation to take place or the member is a virtual member function, the program is ill-formed, no diagnostic required. An implicit instantiation is never generated for an explicit specialization that is declared but not defined.