realloc
<cstdlib>
void * realloc ( void * ptr, size_t size );
Reallocate memory block
The size of the memory block pointed to by the ptr parameter
is changed to the size bytes, expanding or reducing the amount of memory available in the block.The function may move the memory block to a new location, in which case the new location is returned. The content of the memory block is preserved up to the lesser of the new and old sizes, even if the block is moved. If the new size is larger, the value of the newly allocated portion is indeterminate.
In case that ptr is NULL, the function behaves exactly as malloc, assigning a new block of size bytes and returning a pointer to the beginning of it.
In case that the size is 0, the memory previously allocated in ptr is deallocated as if a call to free was made, and a NULL pointer is returned.
Return Value
A pointer to the reallocated memory block, which may be either the same as the ptr argument or a new location.The type of this pointer is void*, which can be cast to the desired type of data pointer in order to be dereferenceable.
If the function failed to allocate the requested block of memory, a NULL pointer is returned, and the memory block pointed to by argument ptr is left unchanged.