Diagnosing an intricate C++ problem

[Gerald Pfeifer <pfeifer at dbai dot tuwien dot ac dot at>]

Consider the following two files, compiled as
  g++ 1.cc 2.cc
and
  g++ 2.cc 1.cc
respectively.

In the first case you'll get 2, in the second 4, instead of the
(originally) expected output of 3.

---- 1.cc ----
struct S {
    int f() { return 1; }
    };

int f1() { S s; return s.f(); }
---- 1.cc ----

---- 2.cc ----
struct S {
    int f() { return 2; }
    };

int f2() { S s; return s.f(); }
int f1();

#include <stdio.h>

main() { printf("%d\n",f1()+f2()); }
---- 2.cc ----

Of course this is a destilled example, but tracking this down in a large
code base took me quite some time and now that template/STL code gets more
and more popular, this is getting more and more likely to bite users.

Being able to issue a warning for such cases would be extremely valuable.

Thoughts?
Gerald
-- 
Gerald "Jerry" pfeifer@dbai.tuwien.ac.at http://www.dbai.tuwien.ac.at/~pfeifer/
Have a look at http://petition.eurolinux.org -- it's not about Linux, btw!