say we have
Class A{};
int *p = malloc(100);
A a; //default constructor in use
*p = A; (question???)
how to initialize an object of type A on alloc memory p?
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bbc
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1Read up on [_placement new_](http://en.wikipedia.org/wiki/Placement_syntax). – ildjarn May 22 '12 at 20:23
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1see http://stackoverflow.com/questions/222557/what-uses-are-there-for-placement-new – bgporter May 22 '12 at 20:25
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Do not use `malloc` in C++. Use `new char[100]` instead. – Mooing Duck May 22 '12 at 20:27
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this is not what I wanted to do, this is an interview question:) – bbc May 22 '12 at 23:53
1 Answers
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To instantiate a class instance at a specific address you need to use placement new.
#include <new>
#include <stdlib.h>
class A
{};
int main()
{
void *p = malloc(100);
A* a = new(p) A();
a->~A(); // call destructor explicitly
free(p);
}
Note that the destructor must be invoked explicitly when using placement new.
Praetorian
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