Abstract Classes in Nios C++

[Altera_Forum]

Hello, 

 I am trying to implement abstract classes using gnupro C++ for nios and cyclone.  Comparing the results using inheritance - and doing wrong - and the virtual keyword - and doing right - in the same code, the code which uses virtual keyword is 15 times bigger.  Does anyone have done something optimized using abstract classes in Nios?  Thanks,  Flavio

[Altera_Forum]

I assume by "abstract classes" you mean classes with pure virtual methods (e.g. virtual int foo() = 0). 

 If you are linking with libstdc++, it could be that a large chunk of exception handling code is being included (I&#39;ve found operator new & delete particularly bad for this and always override them). Have a look at your linker map (if you&#39;re not generating one, add "-Map <filename>" to your linker flags) for any evidence of this. Compiler options "-fno-exceptions" and "-fno-rtti" help greatly in keeping EC++ code size down (assuming you&#39;re not actually using exceptions and run-time type info!).  The code for virtual classes will be bigger due their vtables etc, but not by a factor of 15 (unless the non-virtual ones were very small and numerous).  If your classes really are abstract, try stubbing out the "__cxa_pure_virtual()" function as follows:  extern "C" void __cxa_pure_virtual() { }   Steve.