•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.
