On Thu, 3 Apr 2003, Fred Ma wrote:
> Hello,
>
> I just spent a great number of hours chasing down a
> bug that showed itself on g++ on cygwin, but not on
> g++ on solaris2.5.8. What did it turn out to be?
>
> I had a class member function that returned an
> object, according to the prototype. Also according
> to the function definition. But, the function body
> didn't actually contain a return statement. Like
> SomeFunc() below:
>
> SomeClass{
> // ...
> ReturnType SomeFunc( SomeArgs);
> Void AnotherFunc(void);
> // ...
> }
>
> ReturnType SomeClass::SomeFunc(SomeArgs){
> // Do stuff,
> // No return statement
> }
>
> void SomeClass::AnotherFunc(void){
> // Do stuff...
>
> // Call SomeFunc():
> SomeFunc(SomeArgs);
> }
>
> This caused corruption that resulted in memory
> access violations, even though SomeFunc's
> returned object isn't [EMAIL PROTECTED] point where it
> is invoked. The memory violations didn't happen
> at the point where SomeFunc() was invoked,
> either, but in a later step in the code.
>
> The frustrating thing is that the compiler didn't
> [EMAIL PROTECTED] about the discrepancy between
> the lack of a return statement, even though the
> function needed one. I personally find this kind
> of thing quite common when I reorganize my
> code e.g. moving functionality in and out of class
> member functions; that is, the finger details like
> return types and argument lists change so that
> it's easy to miss.
>
> Shouldn't compilers be smart enough to
> not create code that corrupts when it is pretty
> straighforward to realize that (1) there is an
> obvious discrepancy, for which a warning can
> easily be issued, or (2) realize that the return
> type really isnt' being used and compile it in a
> way that doesn't create memory corruption?
>
> Fred
>
> P.S. Since this happens only on cygwin, it
> might specific to any customizations to g++
> for cygwin. All in all, cygwin's gcc is a much
> better indication of whether my code is buggy,
> because the solaris executables generally
> seem to run fine even when there are cringe-
> inducing bugs, which I only find because they
> crash on cygwin.
Use "g++ -Wall".
Igor
--
http://cs.nyu.edu/~pechtcha/
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|,4- ) )-,_. ,\ ( `'-' Igor Pechtchanski
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Knowledge is an unending adventure at the edge of uncertainty.
-- Leto II
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