Warning: RPG ALIGN not exactly equivalent to C default struct

A warning, for those who use ALIGN on an RPG DS to get the RPG DS
defined equivalently to a C struct.

The C compiler always creates the struct with trailing filler space, so
that the size of the struct is an exact multiple of the alignment.  RPG
does not do this.

For the following C struct, sizeof(s) = 8.
   struct s
   {
      int i;
      char a;
   };

For this apparently matching RPG data structure, %SIZE(s) = 5, not 8.
   D s          DS          align
   D   i             10i 0 
   D   a              1a

If you code DIM(1) on the DS, %SIZE(s1) = 5, but %size(s1:*all) = 8. 
The RPG compiler would allocate 8 bytes for the DIM(1) DS.
   D s1         DS          align dim(1)
   D   i             10i 0 
   D   a              1a

If you are defining an RPG data structure to match a C struct, check the
cross reference to make sure it is an exact multiple of the alignment
size (16 if there is a pointer; 8 if there is an 8-byte integer or
double float; 4 if there is a 4-byte integer or float; 2 if there is a
2-byte integer).

Or write a little C program to get the size of the C struct and make
sure the RPG XREF shows the same length (you can use the "length" entry
on the DS line to get the RPG size correct, or you can add a filler
subfield at the end).

#include <regex.h>
#include <stdio.h>
main()
{
   printf ("%d\n", sizeof(regex_t));
}

Note that this isn't an RPG bug, it's just a difference between C and
RPG.  RPG's ALIGN keyword isn't defined to make the RPG data structure
the same as a C data structure, although it pretty much has that effect
other than in this instance.  (But I know that it _would_ be nice if RPG
had an easy way to define a DS whose size was an exact multiple of its
alignment.)