A #pragma directive to set the behavior for OpenCL extensions.

#pragma OPENCL EXTENSION extension_name : behavior #pragma OPENCL EXTENSION all : behavior



The name of the extension. The extension_name will have names of the form cl_khr_<name> for an extension approved by the OpenCL working group and will have names of the form cl_<vendor_name>_<name> for vendor extensions. The token all means that the behavior applies to all extensions supported by the compiler. The table below shows the legal values for extension_name:

Extension name Description
cl_khr_fp64 Double precision floating-point
cl_khr_select_fprounding_mode Specify rounding mode
cl_khr_global_int32_base_atomics 32-bit global integer base atomic operations
cl_khr_global_int32_extended_atomics 32-bit global integer extended atomic operations
cl_khr_local_int32_base_atomics 32-bit local integer base atomic operations
cl_khr_local_int32_extended_atomics 32-bit local integer extended atomic operations
cl_khr_int64_base_atomics 64-bit integer base atomic operations
cl_khr_int64_extended_atomics 64-bit integer extended atomic operations
cl_khr_3d_image_writes Writes to 3D image objects
cl_khr_byte_addressable_store Allow byte addressible stores
cl_khr_fp16 Half-precision floating-point
CL_APPLE_gl_sharing MacOS X OpenGL sharing
CL_KHR_gl_sharing OpenGL sharing

One of the following values:

behavior Description

Behave as specified by the extension extension_name.

Report an error on the #pragma OPENCL EXTENSION if the
extension_name is not supported, or if all is specified.

disable Behave (including issuing errors and warnings) as if the extension extension_name is not part of the language definition. If all is specified, then behavior must revert back to that of the non-extended core version of the language being compiled to. Warn on the #pragma OPENCL EXTENSION if the extension extension_name is not supported.


The #pragma OPENCL EXTENSION directive is a simple, low-level mechanism to set the behavior for each extension. It does not define policies such as which combinations are appropriate; those must be defined elsewhere. The order of directives matter in setting the behavior for each extension. Directives that occur later override those seen earlier. The all variant sets the behavior for all extensions, overriding all previously issued extension directives, but only if the behavior is set to disable.

The initial state of the compiler is as if the directive #pragma OPENCL EXTENSION all : disable was issued, telling the compiler that all error and warning reporting must be done according to this specification, ignoring any extensions.

Every extension which affects the OpenCL language semantics, syntax or adds built-in functions to the language must create a preprocessor #define that matches the extension name string. This #define would be available in the language if and only if the extension is supported on a given implementation.


An extension which adds the extension string "cl_khr_fp64" should also add a preprocessor #define called cl_khr_fp64. A kernel can now use this preprocessor #define to do something like the following:

#ifdef cl_khr_fp64 // do something using the extension #else // do something else or #error! #endif


OpenCL Specification

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