how to use my_alloc for _all_ new calls in C++?

Question

Imagine I'm in C-land, and I have

 void* my_alloc(size_t size);
 void* my_free(void*);

then I can go through my code and replace all calls to malloc/free with my_alloc/my_free.

How, I know that given a class Foo, I can do placement new; I can also overload the new operator. However, is there a way to do this for all my C++ classes? (i.e. I want to use my own allocator for new and new[]; but I don't want to run through and hack every class I have defined.)

Thanks!

Answer 1

In global scope,

 void* operator new(size_t s) { return my_alloc(s); }
 void operator delete(void* p) { my_free(p); }
 void* operator new[](size_t s) { return my_alloc(s); }
 void operator delete[](void* p) { my_free(p); }

Answer 2

Define custom global new and delete operator functions :

void* operator new(size_t size) 
{
    //do something
    return malloc(size);
}

void operator delete(void *p) 
{
    //do something     
     free(p); 
}

Placement new can be used when you want to create object from the pre-allocated buffer.

Frequent use of new and delete will cause memory fregmentation and it costs to memory access and allocation.So the whole idea of placement new is to create memory pool at the program start and destroy it at program end and all request for memory just returns free memory location from the pool.