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CoTaskMemRealloc function

Changes the size of a previously allocated block of task memory.


LPVOID CoTaskMemRealloc(
  _In_opt_ LPVOID pv,
  _In_     SIZE_T cb


pv [in, optional]

A pointer to the memory block to be reallocated. This parameter can be NULL, as discussed in Remarks.

cb [in]

The size of the memory block to be reallocated, in bytes. This parameter can be 0, as discussed in Remarks.

Return value

If the function succeeds, it returns the reallocated memory block. Otherwise, it returns NULL.


This function changes the size of a previously allocated memory block in the same way that IMalloc::Realloc does. It is not necessary to call the CoGetMalloc function to get a pointer to the OLE allocator before calling CoTaskMemRealloc.

The pv parameter points to the beginning of the memory block. If pv is NULL, CoTaskMemRealloc allocates a new memory block in the same way as the CoTaskMemAlloc function. If pv is not NULL, it should be a pointer returned by a prior call to CoTaskMemAlloc.

The cb parameter specifies the size 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 CoTaskMemRealloc is not guaranteed to be the pointer passed through the pv argument. If pv is not NULL and cb is 0, then the memory pointed to by pv is freed.

CoTaskMemRealloc returns a void pointer to the reallocated (and possibly moved) memory block. The return value is NULL if the size is 0 and the buffer argument is not NULL, or if there is not enough memory available to expand the block to the specified size. In the first case, the original block is freed; in the second case, 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.


Minimum supported client

Windows 2000 Professional [desktop apps | Windows Store apps]

Minimum supported server

Windows 2000 Server [desktop apps | Windows Store apps]

Minimum supported phone

Windows Phone 8







See also




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