PFN_vkAllocationFunction(3)

# PFN_vkAllocationFunction(3) Manual Page

## Name

PFN_vkAllocationFunction - Application-defined memory allocation function

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## C Specification

The type of `pfnAllocation` is:

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

## Parameters

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

- `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 `pfnAllocation` is unable to allocate the requested memory, it must return `NULL`. If the allocation was successful, it must return a valid pointer to memory allocation containing at least `size` bytes, and with the pointer value being a multiple of `alignment`.

Note | Correct Vulkan operation cannot be assumed if the application does not follow these rules. For example, `pfnAllocation` (or `pfnReallocation`) could cause termination of running Vulkan instance(s) on a failed allocation for debugging purposes, either directly or indirectly. In these circumstances, it cannot be assumed that any part of any affected VkInstance objects are going to operate correctly (even vkDestroyInstance), and the application must ensure it cleans up properly via other means (e.g. process termination).

If `pfnAllocation` returns `NULL`, and if the implementation is unable to continue correct processing of the current command without the requested allocation, it must treat this as a runtime error, and generate VK_ERROR_OUT_OF_HOST_MEMORY at the appropriate time for the command in which the condition was detected, as described in Return Codes.

If the implementation is able to continue correct processing of the current command without the requested allocation, then it may do so, and must not generate VK_ERROR_OUT_OF_HOST_MEMORY as a result of this failed allocation.

## 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