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Memory management - virtual function table

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Im not using 'new' to allocate memory in my app, only casting a chunk of memory from a big pool pre-alocated....it works for classes that do not inherit from another ones... How do i fill the VFT after alocating a "generic" memory to a variable? I read somewhere to do something like cCLASS_A *a = (cCLASS_A*)my_mem_sys.Alocate(sizeof(cCLASS_a)); a = new (cCLASS_A*); //something like this, i really dont know Im trying to do not allocate any memory in conventional way, to avoid fragmentation...and about using the method above to fill the VFT, does it allocate any memory? Thanks

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Use placement new:

class C
{
};

void* data = malloc(sizeof C);
C* c = new(data) C(); // run ctor, should fill out VFT as well

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It won't allocate any memory from the heap, if that's what you're asking. However, it does call the class's constructor, so if the constructor calls new/malloc()/whatever, then additional memory will be allocated.

Just remember to call the destructor when you're done with it. Using antareus' example, the syntax would look like:
c->~C();

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