NAME

       Restrictions

       •   The use of pointers is somewhat restricted. The following rules apply:

           •   Arguments to functionQualifiers(3clc) functions declared in a program that are pointers must be
               declared with the global(3clc), constant(3clc), or local(3clc) qualifier.

           •   A pointer declared with the constant(3clc), local(3clc), or global(3clc) qualifier can only be
               assigned to a pointer declared with the __constant, __local, or __global qualifier respectively.

           •   Pointers to functions are not allowed.

           •   Arguments to functionQualifiers(3clc) functions in a program cannot be declared as a pointer to a
               pointer(s). Variables inside a function or arguments to non-kernel functions in a program can be
               declared as a pointer to a pointer(s).

       •   An image type ( otherDataTypes(3clc), otherDataTypes(3clc), otherDataTypes(3clc),
           otherDataTypes(3clc), otherDataTypes(3clc), or otherDataTypes(3clc)) can only be used as the type of
           a function argument. An image function argument cannot be modified. Elements of an image can only be
           accessed using the imageFunctions(3clc).

           An image type cannot be used to declare a variable, a structure or union field, an array of images, a
           pointer to an image, or the return type of a function. An image type cannot be used with the
           private(3clc), local(3clc) and constant(3clc) address space qualifiers. The otherDataTypes(3clc) type
           cannot be used with the __write_only access qualifier unless the cl_khr_3d_image_writes(3clc)
           extension is enabled. An image type cannot be used with the accessQualifiers(3clc) access qualifer
           which is reserved for future use.

           The sampler type (sampler_t(3clc)) can only be used as the type of a function argument or a variable
           declared in the program scope or the outermost scope of a kernel function. The behavior of a sampler
           variable declared in a non-outermost scope of a kernel function is implementation-defined. A sampler
           argument or variable cannot be modified.

           The sampler type cannot be used to declare a structure or union field, an array of samplers, a ponter
           to a sampler, or the return type of a function. The sampler type cannot be used with the __local and
           __global address space qualifiers.

       •   Bit-fields struct members are currently not supported.

       •   Variable length arrays and structures with flexible (or unsized) arrays are not supported.

       •   Variadic macros and functions are not supported.

       •   The library functions defined in the C99 standard headers assert.h, ctype.h, complex.h, errno.h,
           fenv.h, float.h, inttypes.h, limits.h, locale.h, setjmp.h, signal.h, stdarg.h, stdio.h, stdlib.h,
           string.h, tgmath.h, time.h, wchar.h, and wctype.h are not available and cannot be included by a
           program.

       •   The auto and register storage-class specifiers are not supported.

       •   Recursion is not supported.

       •   The function using the functionQualifiers(3clc) qualifier can only have return type void in the
           source code.

       •   Arguments to kernel functions in a program cannot be declared with the built-in scalar types bool,
           half, size_t, ptrdiff_t, intptr_t, and uintptr_t, or a struct and/or union that contain fields
           declared to be one of these built-in scalar types. The size in bytes of these types except half are
           implementation-defined and in addition can also be different for the OpenCL device and the host
           processor making it difficult to allocate buffer objects to be passed as arguments to a kernel
           declared as pointer to these types.  half is not supported as half can be used as a storage format
           only (unless the cl_khr_fp16(3clc) extension is supported) and is not a data type on which
           floating-point arithmetic can be performed.

       •   Whether or not irreducible control flow is illegal is implementation defined.

       •   Arguments to kernel functions in a program cannot be declared to be of type otherDataTypes(3clc).

       •   Elements of a struct or union must belong to the same address space. Declaring a struct or union
           whose elements are in different address spaces is illegal.

       •   Arguments to kernel functions that are declared to be a struct or union do not allow OpenCL objects
           to be passed as elements of the struct or union.

       •   The type qualifiers const, restrict, and volatile as defined by the C99 specification are supported.
           These qualifiers cannot be used with otherDataTypes(3clc), otherDataTypes(3clc),
           otherDataTypes(3clc), otherDataTypes(3clc), otherDataTypes(3clc), and otherDataTypes(3clc) types.
           Types other than pointer types shall not use the restrict qualifier.

       •   The event type (otherDataTypes(3clc)) cannot be used as the type of a kernel function argument. The
           event type cannot be used to declare a program scope variable. The event type cannot be used to
           declare a structure or union field. The event type cannot be used with the local(3clc),
           constant(3clc), and global(3clc) address space qualifiers.

SPECIFICATION

       OpenCL Specification[1]

SEE ALSO

       imageFunctions(3clc), functionQualifiers(3clc)

AUTHORS

       The Khronos Group

COPYRIGHT

       Copyright © 2007-2011 The Khronos Group Inc.
       Permission is hereby granted, free of charge, to any person obtaining a copy of this software and/or
       associated documentation files (the "Materials"), to deal in the Materials without restriction, including
       without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
       copies of the Materials, and to permit persons to whom the Materials are furnished to do so, subject to
       the condition that this copyright notice and permission notice shall be included in all copies or
       substantial portions of the Materials.

NOTES

        1. OpenCL Specification
           page 231, section 6.9 - Restrictions