Prev: wide codecvt not used unless sync_with_stdio(false)
Next: Adapting code for C++98 compliance.
From: nils.hjelte on 7 May 2008 02:43
Hi!

Not really sure where to post this, maybe the gcc list instead?

Anyway, if I have two cpp files with identical class declarations (but
with different semantics) of an internal class, and link them
together, one of the implementations get thrown out without any kind
of warning.

Simple example:

foo.cpp
=========================================

#include <iostream>

class DuplicateClass
{
public:
void foo() { std::cout << "foo" << std::endl; }
void foobar() { std::cout << "first foobar" << std::endl; }
};

void foo()
{
DuplicateClass test;
test.foo();
test.foobar();
}


bar.cpp
=========================================
#include <iostream>

class DuplicateClass
{
public:
void bar() { std::cout << "bar" << std::endl; }
void foobar() { std::cout << "second foobar" << std::endl; }
};

void bar()
{
DuplicateClass test;
test.bar();
test.foobar();
}

main.cpp
==========================================
void foo();
void bar();

int main (int argc, char const *argv[])
{
foo();
bar();
return 0;
}



Compiled with

g++ -o test main.cpp foo.cpp bar.cpp -Wall

I get the following output when executing the program

foo
first foobar
bar
first foobar

The test.foobar() call in bar.cpp should output 'second foobar' not
'first foobar'. Looking at the symbols in the executable file it is
obvious that one of the colliding symbols have been thrown out (only
one foobar entry):

$ nm test | grep DuplicateClass
00001c96 T __ZN14DuplicateClass3barEv
00001bce T __ZN14DuplicateClass3fooEv
00001c12 T __ZN14DuplicateClass6foobarEv

Why won't the compiler/linker give me a warning/error when doing this?
I had a really nasty bug resulting from this, which was pretty
difficult to track down. I tried declaring the classes with 'static
class' thinking it would work as 'static function' does in C, but it
is obviously not valid C++ syntax.

Is it not possible to limit the scope of the class to the local cpp
file? And why does not the compiler provide a warning when this
happens??

--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

 | 
Pages: 1
Prev: wide codecvt not used unless sync_with_stdio(false)
Next: Adapting code for C++98 compliance.