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Re: Missing virtual functions
- To: ebritten at uci dot edu
- Subject: Re: Missing virtual functions
- From: Fergus Henderson <fjh at cs dot mu dot OZ dot AU>
- Date: Mon, 1 Sep 1997 12:53:57 +1000 (EST)
- Cc: gnu-win32 at cygnus dot com
- References: <33FF524B.7B256D82@uci.edu>
This is an off-topic answer to an off-topic question about GNU C++.
Eric Britten <ebritten@uci.edu> writes:
>Yesterday I found that if one declares virtual functions in a class
>like:
>
>class A
>{
> A();
> virtual void B();
>};
>
>and the definitions for the functions(inline or external) are not found
>by the linker then two types of linking errors result.
>
>1. Undefined reference to a vtable in the constructors of the class.
>2. Undefined reference to any other inline functions of the class that
>are used by other code.
>
>It took me a while to figure out that if all virtual functions are
>defined, then these errors go away. Is this GNU specific?
The exact error messages you get are probably specific to GNU C++.
However, the fact that you do get errors if virtual functions
are not defined is not GNU specific. The GNU behaviour conforms
to the draft ANSI/ISO C++ standard, which says that programs must
contain a definition of every virtual function. (Implementations
are not _required_ to diagnose this error, however, so such code
_may_ work on other compilers...)
--
Fergus Henderson <fjh@cs.mu.oz.au> | "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh> | of excellence is a lethal habit"
PGP: finger fjh@128.250.37.3 | -- the last words of T. S. Garp.
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