[Bug c++/51757] New: friend defined inside class and declared inside main linker error

[Bug c++/51757] New: friend defined inside class and declared inside main linker error

[neotheone222 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51757

             Bug #: 51757
           Summary: friend defined inside class and declared inside main
                    linker error
    Classification: Unclassified
           Product: gcc
           Version: 4.5.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: neotheone222@gmail.com


--------------------------------------------------------------------------------
gcc -v:

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.5.2-8ubuntu4' --with-bugurl=file:///usr/share/doc/gcc-4.5/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.5 --enable-shared --enable-multiarch
--with-multiarch-defaults=x86_64-linux-gnu --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib/x86_64-linux-gnu
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.5 --libdir=/usr/lib/x86_64-linux-gnu
--enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-plugin --enable-gold --enable-ld=default
--with-plugin-ld=ld.gold --enable-objc-gc --disable-werror --with-arch-32=i686
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.5.2 (Ubuntu/Linaro 4.5.2-8ubuntu4) 

gcc command: g++ 1.cpp

gcc output: 

/tmp/cc9Q9mFy.o: In function `main':
1.cpp:(.text+0x5): undefined reference to `func()'
collect2: ld returned 1 exit status

--------------------------------------------------------------------------------

Here is the program that fails to link:

                                //1.cpp
#include <iostream>

class A
{
  public:
    friend void
    func()
    {
      std::cout << "Called" << std::endl;
    }
};

int
main()
{
  void
  func();

  func();   //linker error undefined reference to `func()'

  return 0;
}

[Bug c++/51757] friend defined inside class and declared inside main linker error

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51757

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-05 01:34:21 UTC ---
Curious. It still fails even if there is a declaration of func at namespace
scope.

It works with -fkeep-inline-functions

[Bug c++/51757] friend defined inside class and declared inside main linker error

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51757

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-01-05 09:39:28 UTC ---
Hm?  How should it _not_ fail to link?  You declare void func() inside
main which puts it in ::, but there is no definition.  Obviously
A::func() is not found by lookup - why should it?

[Bug c++/51757] friend defined inside class and declared inside main linker error

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51757

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
   Last reconfirmed|                            |2012-01-05
         Resolution|INVALID                     |
     Ever Confirmed|0                           |1

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-05 10:35:56 UTC ---
There is no A::func, that's a friend not a member function. 

[class.friend]

-6-  A function can be defined in a friend declaration of a class if and only
if the class is a non-local class (9.8), the function name is unqualified, and
the function has namespace scope. [ Example:
class M {
  friend void f() { } // definition of global f, a friend of M,
                      // not the definition of a member function
};
—end example ]
-7- Such a function is implicitly inline. A friend function defined in a class
is in the (lexical) scope of the class in which it is defined. A friend
function defined outside the class is not (3.4.1).

[Bug c++/51757] friend defined inside class and declared inside main linker error

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51757

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-05 10:42:56 UTC ---
Also, if there's no definition, why would it link when -fkeep-inline-functions
is used?  My guess would be that the call in main doesn't mark the inline
function as used, so it is not emitted.

For the record, Solaris CC fails in the same way, it links OK with clang++

[Bug c++/51757] friend defined inside class and declared inside main linker error

[language.lawyer at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51757

Language Lawyer <language.lawyer at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |language.lawyer at gmail dot com

--- Comment #6 from Language Lawyer <language.lawyer at gmail dot com> ---
No linker error in GCC 11.0.0 20210117 (experimental)
https://wandbox.org/permlink/EXabQxhTzbDzvbvr

[Bug c++/51757] friend defined inside class and declared inside main linker error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51757

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.0
         Resolution|---                         |FIXED
             Status|REOPENED                    |RESOLVED

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed by r11-3699-g4e62aca0e0520e4e .