__alignof__(3) - NetBSD Manual Pages

__ALIGNOF__(3)          NetBSD Library Functions Manual         __ALIGNOF__(3)


NAME

     __alignof__ -- GNU extension for alignment of an object


SYNOPSIS

     int
     __alignof__(void x);


DESCRIPTION

     The __alignof__() operator returns the alignment of its operand.  The op-
     erand can be a type or an expression.  If the operand is a `lvalue', the
     return value represents the required alignment of the underlying type,
     not the actual alignment of the specified `lvalue'.

     The returned value is specific to the architecture and the ABI.  If the
     architecture does not impose strict alignment requirements, __alignof__()
     returns the minimum required alignment.  If __aligned(3) is used to
     increase the alignment, __alignof__() returns the specified alignment.


EXAMPLES

     The syntax is comparable to the sizeof() operator.  If the architecture
     aligns integers along 32-bit address boundaries, the following should
     print the value 4.

           (void)printf("%d\n", __alignof__(int));

     On the other hand, the following example should print the value 1, even
     though this is unlikely to be the actual alignment of the structure mem-
     ber.

           struct align {
                   int  x;
                   char y;
           } a;

           (void)printf("%d\n", __alignof__(a.y));


SEE ALSO

     gcc(1), attribute(3), offsetof(3), typeof(3)


CAVEATS

     This is a non-standard, compiler-specific extension.

NetBSD 9.2                     December 20, 2010                    NetBSD 9.2