[cfe-dev] [Bug] Undefined reference to function template declared friend and defined in template class

[John McCall]

On Mar 10, 2014, at 9:07 AM, suyog sarda <sardask01 at gmail.com> wrote:
> This is regarding g++ test case 
> g++.old-deja/g++.pt/friend10.C
> 
> template <class T>
> void f(T);
> 
> template <class U>
> class C
> { 
>   template <class T>
>   friend void f(T)
>   {
>      C<U> c;
>      c.i = 3;
>   }
> 
>   public :
> 
>      void g()
>      {
>        f(3.0);
>      }
>     int i;
> };
> 
> int main ()
> {
>   f(7);
>   C<double> c;
>   c.g();
> }
> 
> Here, even when the body of function f() is defined, compiler throws error :
> 
> In function `main':
> 19095.C:(.text+0x16): undefined reference to `void f<int>(int)'
> /tmp/19095-fd27b4.o: In function `C<double>::g()':
> 19095.C:(.text._ZN1CIdE1gEv[_ZN1CIdE1gEv]+0x1b): undefined reference to `void f<double>(double)'
> clang-3.5: error: linker command failed with exit code 1
> 
> I have filed a bug related to this llvm.org/bugs/show_bug.cgi?id=19095
> 
> g++ compiles this without any error.
> 
> Please help in verifying if above is real bug. In my view this is a bug since function body has been defined and as it is declared friend it is a non-member function of class template.

It does look like a bug.  Note that you can only instantiate this class template once, since the second instantiation would introduce a redefinition of f.

John.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20140311/ba417187/attachment.html>