XL Fortran Enterprise Edition for AIX : User's Guide - IBM

a derived type are stored with sufficient padding that components
will be stored on their natural alignment boundaries, unless
storage association requires otherwise. The natural alignment
boundaries for objects of a type that appears in the left-hand
column of the following table is shown in terms of a multiple of
some number of bytes in the corresponding entry in the right-hand
column of the table.
Type
Natural Alignment (in
multiples of bytes)
INTEGER(1), LOGICAL(1), BYTE, CHARACTER 1
INTEGER(2), LOGICAL(2) 2
INTEGER(4), LOGICAL(4), REAL(4) 4
INTEGER(8), LOGICAL(8), REAL(8), COMPLEX(4) 8
REAL(16), COMPLEX(8), COMPLEX(16) 16
Derived
Maximum alignment of its
components
port
If the natural suboption of the struct option is specified, arrays of
derived type are stored so that each component of each element is
stored on its natural alignment boundary, unless storage
association requires otherwise.
If the port suboption of the struct option is specified,
v
v
Storage padding is the same as described above for the natural
suboption, with the exception that the alignment of components
of type complex is the same as the alignment of components of
type real of the same kind.
The padding for an object that is immediately followed by a
union is inserted at the begining of the first map component for
each map in that union.
Restrictions
The port suboption does not affect any arrays or structures with the AUTOMATIC
attribute or arrays that are allocated dynamically. Because this option may change
the layout of non-sequence derived types, when compiling programs that read or
write such objects with unformatted files, use the same setting for this option for
all source files.
You must use -qalign=4k if you are using the I/O techniques that are described in
“Increasing Throughput with Logical Volume I/O and Data Striping” on page 333.
Related Information
You can tell if an array has the AUTOMATIC attribute and is thus unaffected by
-qalign=4k if you look for the keywords AUTOMATIC or CONTROLLED
AUTOMATIC in the listing of the “-qattr Option” on page 133. This listing also
shows the offsets of data objects.
126 XL Fortran Enterprise Edition for AIX : User’s Guide