Hi,
Are there any hidden costs to using virtual functions in C++ classes using
the PRC tools? (I know about the GCC compiler and linker switches to disable
exceptions and RTTI.)
I know that polymorphism requires an in-memory table to ensure that the
correct functions get called at run-time (late binding) and that this eats
into the available heap size. However, I want to use pure virtual functions
in my classes solely to specify a contract that subclasses must abide to. I
will not use base class pointers, only pointers to non-abstract classes.
Example:
-----------------------------------------------
class BaseClass {
protected:
int a;
public:
virtual void add(int a) = 0; // Pure virtual function
};
class DerivedClass: public BaseClass {
public:
DerivedClass(int a) {
this->a = a;
}
void add(int a); // Implementation omitted
};
BaseClass* a = new DerivedClass(1);
a->add(1); // Polymorphism, late binding
DerivedClass* b = new DerivedClass(1);
b->add(1); // No polymorphism(?), early binding(?)
-----------------------------------------------
I have a gut feeling that the GCC compiler is smart enough to resolve the
function call for "b" at compile-time, hence no need for a function table at
run-time, but I'm not sure. (It's been years since I last used C/C++ for a
large project.)
Also, how much memory does polymorphism actually require? Should you really
avoid it at all costs on Palm OS? My target is OS 3.5+ running on 4Mb+
devices.
Thanks
-Laurens
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