Re: [avr-gcc-list] Problems with abstract classes / pure virtual functions:

[René Liebscher]

address@hidden schrieb:

> Hi!
> I got a somehow mysterious (hopefully not to silly) problem involving 
> abstract classes.
> Here a test:
>
> class abstract_base
> {
> public:
> virtual void testfunction(void)=0;
> virtual ~abstract_base(){} *
> };
>
> class concrete_class : public abstract_base
> {
> public:
> void testfunction(void){}
> ~concrete_class(){}
> };
>
> Now I do the following:
>
> int main(void)
> {
> concrete_class testobject;
> }
>
> And the Compiler warns me about:
>
> warning: alignment of 'concrete_class::_ZTV14concrete_class' is 
> greater than maximum object file alignment. Using 1
> warning: alignment of 'abstract_base::_ZTV13abstract_base' is greater 
> than maximum object file alignment. Using 1
This is normally not a problem I had this warnings all the time but 
programs run withput problems.

> And the Linker finally generates an error:
> ....h:8: undefined reference to `__cxa_pure_virtual' ( which is 
> actually the line marked by *)
I get this error with GCC 3.4
$avr-gcc --version
avr-gcc (GCC) 3.4.3
This is a problem in gcc 3.4.
The same program with gcc (3.3.?) didn't show this error.

-O1 should work.

For  more optimization try to use the option -fno-unit-at-a-time for the 
compiler.

Kind regards
Rene Liebscher

> If You have any clues, why that problem shows up, please give me a hint.
> Thancs a lot
> Thomas