156. Polymorphism-i

Question.4

A developer compares two versions of a GPIO class:

class GPIO_NoVirtual { int pin; };
class GPIO_Virtual  { int pin; virtual void write(bool) {} };

printf("%zu %zu",
   sizeof(GPIO_NoVirtual),
   sizeof(GPIO_Virtual));

On a 32-bit ARM, what is the likely output?

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4 4 -- virtual adds no overhead
4 8 -- the virtual class gets a hidden vptr (4 bytes) pointing to the vtable
4 12 -- virtual adds both vptr and vtable inline
8 8 -- both have padding

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