(gcc-300.info)Alignment


Inquiring on Alignment of Types or Variables
============================================

   The keyword `__alignof__' allows you to inquire about how an object
is aligned, or the minimum alignment usually required by a type.  Its
syntax is just like `sizeof'.

   For example, if the target machine requires a `double' value to be
aligned on an 8-byte boundary, then `__alignof__ (double)' is 8.  This
is true on many RISC machines.  On more traditional machine designs,
`__alignof__ (double)' is 4 or even 2.

   Some machines never actually require alignment; they allow reference
to any data type even at an odd addresses.  For these machines,
`__alignof__' reports the _recommended_ alignment of a type.

   If the operand of `__alignof__' is an lvalue rather than a type, its
value is the required alignment for its type, taking into account any
minimum alignment specified with GCC's `__attribute__' extension (Note:
Variable Attributes).  For example, after this declaration:

     struct foo { int x; char y; } foo1;

the value of `__alignof__ (foo1.y)' is 1, even though its actual
alignment is probably 2 or 4, the same as `__alignof__ (int)'.

   It is an error to ask for the alignment of an incomplete type.


automatically generated by info2www version 1.2.2.9