(gcc.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.
 
    When the operand of `__alignof__' is an lvalue rather than a type,
 the value is the largest alignment that the lvalue is known to have.
 It may have this alignment as a result of its data type, or because it
 is part of a structure and inherits alignment from that structure.  For
 example, after this declaration:
 
      struct foo { int x; char y; } foo1;
 
 the value of `__alignof__ (foo1.y)' is probably 2 or 4, the same as
 `__alignof__ (int)', even though the data type of `foo1.y' does not
 itself demand any alignment.
 
    A related feature which lets you specify the alignment of an object
 is `__attribute__ ((aligned (ALIGNMENT)))'; see the following section.

Info Catalog

(gcc.info) Type Attributes

(gcc.info) C Extensions

(gcc.info) Inline

automatically generated byinfo2html