Changes the size of a previously allocated memory block.

  • oid *Realloc(

void *pv,
//The memory block to be reallocated
//The size of the memory block in bytes



[in] Points to the memory block to be reallocated. It can be a NULL pointer, as discussed in the following Comments section.


[in] Specifies the size of the memory block (in bytes) to be reallocated. It can be zero, as discussed in the following remarks.

Return Values

Reallocated memory block

Memory block successfully reallocated.


Insufficient memory or cb is zero and pv is not NULL.


The initial contents of the returned memory block are undefined - there is no guarantee that the block has been initialized, so you should initialize it in your code. The allocated block may be larger than cb bytes because of the space required for alignment and for maintenance information.

The pv argument points to the beginning of the memory block. If pv is NULL, IMalloc::Realloc allocates a new memory block in the same way as IMalloc::Alloc. If pv is not NULL, it should be a pointer returned by a prior call to IMalloc::Alloc.

The cb argument specifies the size (in bytes) of the new block. The contents of the block are unchanged up to the shorter of the new and old sizes, although the new block can be in a different location. Because the new block can be in a different memory location, the pointer returned by IMalloc::Realloc is not guaranteed to be the pointer passed through the pv argument. If pv is not NULL and cb is zero, then the memory pointed to by pv is freed.

IMalloc::Realloc returns a void pointer to the reallocated (and possibly moved) memory block. The return value is NULL if the size is zero and the buffer argument is not NULL, or if there is not enough memory available to expand the block to the given size. In the first case, the original block is freed; in the second, the original block is unchanged.

The storage space pointed to by the return value is guaranteed to be suitably aligned for storage of any type of object. To get a pointer to a type other than void, use a type cast on the return value.

See Also

IMalloc::Alloc, IMalloc::Free

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