C Specification

A collection of 64-bit flags is represented by a bitmask using the type VkFlags64:

// Provided by VK_VERSION_1_3, VK_KHR_synchronization2
typedef uint64_t VkFlags64;


When the 31 bits available in VkFlags are insufficient, the VkFlags64 type can be passed to commands and structures to represent up to 64 options. VkFlags64 is not used directly in the API. Instead, a Vk*Flags2 type which is an alias of VkFlags64, and whose name matches the corresponding Vk*FlagBits2 that are valid for that type, is used.

Any Vk*Flags2 member or parameter used in the API as an input must be a valid combination of bit flags. A valid combination is either zero or the bitwise OR of valid bit flags.

An individual bit flag is valid for a Vk*Flags2 type if it would be a valid enumerant when used with the equivalent Vk*FlagBits2 type, where the bits type is obtained by taking the flag type and replacing the trailing Flags2 with FlagBits2. For example, a flag value of type VkAccessFlags2KHR must contain only bit flags defined by VkAccessFlagBits2KHR.

Any Vk*Flags2 member or parameter returned from a query command or otherwise output from Vulkan to the application may contain bit flags undefined in its corresponding Vk*FlagBits2 type. An application cannot rely on the state of these unspecified bits.


Both the Vk*FlagBits2 type, and the individual bits defined for that type, are defined as uint64_t integers in the C API. This is in contrast to the 32-bit types, where the Vk*FlagBits type is defined as a C enum and the individual bits as enumerants belonging to that enum. As a result, there is less compile time type checking possible for the 64-bit types. This is unavoidable since there is no sufficiently portable way to define a 64-bit enum type in C99.

See Also

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.

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