Searching for duplicates currently gives:
- This post which specifically treats the case of a Singleton implementation, and in which the answers avoids the warning altogether with a different implementation.
- This post which answers itself without solving the issue.
- A suggested duplicate which explains how to implement template member functions (not relevant).
- Another suggested duplicate explaining how to define template static members (not relevant).
As far as I understand, none of these answers the question of how to get rid of Wundefined-var-template
with clang++ 3.8+ in a situation similar to the MCVE below?
File a.h
#ifndef A_INCLUDED
#define A_INCLUDED
template <class T>
struct A
{
static const char *name;
};
#endif
File a.cpp
#include "a.h"
template <> const char* A<double>::name = "Johnny";
template <> const char* A<float>::name = "Dude";
File b.cpp
#include <cstdio>
#include "a.h"
void say_it() {
printf( "%s\n", A<double>::name );
}
Run from a terminal:
$ clang++ -c -o a.o -std=c++11 a.cpp
$ clang++ -c -o b.o -std=c++11 b.cpp a.o
clang: warning: a.o: 'linker' input unused [-Wunused-command-line-argument]
b.cpp:5:32: warning: instantiation of variable 'A<double>::name' required here, but no definition is available [-Wundefined-var-template]
printf( "%s\n", A<double>::name );
^
./a.h:7:28: note: forward declaration of template entity is here
static const char *name;
^
b.cpp:5:32: note: add an explicit instantiation declaration to suppress this warning if 'A<double>::name' is explicitly instantiated in another translation unit
printf( "%s\n", A<double>::name );
^
1 warning generated.
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