Helper Macros

General useful language macros More...

Macros
#define	__build_assert(cond)
	Assert a build-time dependency.
#define	__build_assert_or_zero(cond)
	Assert a build-time dependency.
#define	__array_size(arr)
	Get the number of elements in a visible array.
#define	_array_size_chk(arr)
#define	__stringify(arg)
	Create a string from the argument.
#define	__is_defined(macro)
	Check if a macro is defined to 1.

Detailed Description

General useful language macros

This group contains definitions to help give robust solutions to common code patterns.

Macro Definition Documentation

__array_size

#define __array_size

(

arr

)

Value:

(sizeof(arr) / sizeof((arr)[0]) + _array_size_chk(arr))

Get the number of elements in a visible array.

This does not work on pointers, or arrays declared as [], or function parameters. With correct compiler support, such usage will cause a build error (

See also

__build_assert).

Parameters

arr	The array whose size you want.

__build_assert

#define __build_assert

(

cond

)

Value:

    do { (void) sizeof(char [1 - 2*!(cond)]); } while(0)

Assert a build-time dependency.

Your compiler will fail if the condition isn't true, or can't be evaluated by the compiler. This can only be used within a function.

Example: #include <stddef.h> ... static char *foo_to_char(struct foo *foo) { This code needs string to be at start of foo. __build_assert(offsetof(struct foo, string) == 0); return (char *)foo; }

Parameters

cond	The compile-time condition which must be true.

See also

__build_assert_or_zero

__build_assert_or_zero

#define __build_assert_or_zero

(

cond

)

Value:

    (sizeof(char [1 - 2*!(cond)]) - 1)

Assert a build-time dependency.

Your compiler will fail if the condition isn't true, or can't be evaluated by the compiler. This can be used in an expression: its value is "0".

Example: #define foo_to_char(foo) \ ((char *)(foo) \

• __build_assert_or_zero(offsetof(struct foo, string) == 0))

Parameters

cond	The compile-time condition which must be true.

See also

__build_assert

__is_defined

#define __is_defined

(

macro

)

Value:

!__builtin_strcmp(__stringify(macro), "1")

Check if a macro is defined to 1.

Parameters

macro

The macro to check

Returns

1 if the macro is defined to 1, 0 otherwise.

__stringify

#define __stringify

(

arg

)

Value:

""#arg

Create a string from the argument.

Parameters

arg	The text to stringify.

_array_size_chk

#define _array_size_chk

(

arr

)

Value:

    __build_assert_or_zero(!__builtin_types_compatible_p(typeof(arr),   \
                            typeof(&(arr)[0])))