[Bug 305460]

[Redi]

(In reply to Jonathan Wakely from comment #3)
> The linker error alone doesn't make the root cause obvious, but it's a
> fairly well known and well documented problem:
> http://www.parashift.com/c++-faq-lite/strange-inheritance.html#faq-23.10

A better link is now:
https://gcc.gnu.org/wiki/VerboseDiagnostics#undefined_reference_to_vtable_for_X

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https://bugs.launchpad.net/bugs/305460

Title:
  [PR42540] c++ error message [vtable undefined] is unhelpful

Status in gcc:
  In Progress
Status in gcc-defaults package in Ubuntu:
  Confirmed

Bug description:
  I've had response to g++ crash reports, so maybe you'd also like to
  know about this confusing error message I found.

  Thanks!
  Alan

  This is on an up-to-date install of "Ubuntu 8.04.1".

  apt-cache policy gcc
  gcc:
    Installed: 4:4.2.3-1ubuntu6
    Candidate: 4:4.2.3-1ubuntu6
    Version table:
   *** 4:4.2.3-1ubuntu6 0
          500 http://gb.archive.ubuntu.com hardy-updates/main Packages
          100 /var/lib/dpkg/status
       4:4.2.3-1ubuntu3 0
          500 http://gb.archive.ubuntu.com hardy/main Packages


  Minimal test program:

  class A {
      A();

      virtual void B();
  };

  A::A() {}
  /* Whoops, I forgot to define A::B() */

  Actual error message:

  /usr/lib/gcc/x86_64-linux-gnu/4.2.4/../../../../lib/crt1.o: In function `_start':
  (.text+0x20): undefined reference to `main'
  /tmp/cc8P2uDq.o: In function `A::A()':
  test.cpp:(.text+0x9): undefined reference to `vtable for A'
  /tmp/cc8P2uDq.o: In function `A::A()':
  test.cpp:(.text+0x1f): undefined reference to `vtable for A'
  collect2: ld returned 1 exit status

  Expected error message:

  Something more like "undefined reference to A::B()"

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