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