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 operand 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 member.
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.