PFN_vkReallocationFunction(3)

# PFN_vkReallocationFunction(3) Manual Page

## Name

PFN_vkReallocationFunction - Application-defined memory reallocation function

## C Specification

The type of `pfnReallocation` is:

    // Provided by VK_VERSION_1_0
    typedef void* (*PFN_vkReallocationFunction)(
        void*                                       pUserData,
        void*                                       pOriginal,
        size_t                                      size,
        size_t                                      alignment,
        VkSystemAllocationScope                     allocationScope);

## Parameters

- `pUserData` is the value specified for VkAllocationCallbacks::`pUserData` in the allocator specified by the application.

- `pOriginal` must be either `NULL` or a pointer previously returned by `pfnReallocation` or `pfnAllocation` of a compatible allocator.

- `size` is the size in bytes of the requested allocation.

- `alignment` is the requested alignment of the allocation in bytes and must be a power of two.

- `allocationScope` is a VkSystemAllocationScope value specifying the allocation scope of the lifetime of the allocation, as described here.

## Description

If the reallocation was successful, `pfnReallocation` must return an allocation with enough space for `size` bytes, and the contents of the original allocation from bytes zero to min(original size, new size) - 1 must be preserved in the returned allocation. If `size` is larger than the old size, the contents of the additional space are undefined. If satisfying these requirements involves creating a new allocation, then the old allocation should be freed.

If `pOriginal` is `NULL`, then `pfnReallocation` must behave equivalently to a call to PFN_vkAllocationFunction with the same parameter values (without `pOriginal`).

If `size` is zero, then `pfnReallocation` must behave equivalently to a call to PFN_vkFreeFunction with the same `pUserData` parameter value, and `pMemory` equal to `pOriginal`.

If `pOriginal` is non-`NULL`, the implementation must ensure that `alignment` is equal to the `alignment` used to originally allocate `pOriginal`.

If this function fails and `pOriginal` is non-`NULL` the application must not free the old allocation.

`pfnReallocation` must follow the same rules for return values as `PFN_vkAllocationFunction`.

## See Also

VK_VERSION_1_0, VkAllocationCallbacks, VkSystemAllocationScope

## Document Notes

For more information, see the Vulkan Specification.

This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.

## Copyright

Copyright 2014-2026 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0