Re: C++ pure virtual base class memory consumption

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

On 08/20/2012 08:52 PM, fueb wrote:
> Hi out there, I hope someone can give me a hint on a problem building a c++
> static library using newlib and lpcxpresso. Everything works fine, but I
> have a size-problem.
>
> I have got a class that has pure virtual methods. Another class derives this
> base class and implements the function:
>
> Code:
>
> class A {
>   public:
>     virtual void method() = 0;
> }
> class B : public A {
>     virtual void method() { // do something }
>   }
>
> Using the above code links appr. 60kB more code from newlib into the
> application than if I use the following code, where the base class method is
> already implemented but overwritten in the derived class:

Are you sure this code is from Newlib and not GCC?

> Code:
>
> class A {
>   public:
>     virtual void method() {} // <-- the only change
> }
> class B : public A {
>     virtual void method() { // do something }
> }
>
> I know that gcc for other small devices is capable to build this with
> smaller code, probably with a commandline switch, but I do not know how.
>
> Does someone have a hint on how I could prevent the compiler to
> auto-implement that much functions used for the pure virtual class?

I suppose this is due to the abort handler with pretty printing pulled in by a 
pure virtual function.  You should look at the map file of the linker.  See also

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43852

--
Sebastian Huber, embedded brains GmbH

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