AIX Version 4.3 Differences Guide

These ANSI types are defined through the header . Note that the
signed or unsigned are explicitly coded into the typedefs and not left to chance.
Although it is unlikely that the defaults for short/int/long are unsigned, it is
possible on some machines. Furthermore, by forcing the keyword, this would
have the same error behavior in all cases if the user were to add a sign qualifier
to the ANSI types, as in signed int8_t.
3.3.1.3 Structure Alignment and Bitfields
The LP64 specifications will change the size, member alignment, structure
alignment, and bitfield sizes and alignment of most structures implicitly.
Structures with only long and pointer types will at least double in size depending
on the alignment mode.
Sharing data between 64-bit and 32-bit processes will not be possible unless the
fixed-width types are used, or the structure is devoid of pointer and long types.
Special attention needs to be paid to unions that attempt to overlay int types with
long types or pointer types.
For the details of alignment in different modes and in combination with different
compiler flags, consult the compiler reference manual.
Table 15 provides the different alignments found in 32- or 64-bit modes.
Table 15. Alignment of Basic Data Types in 32- and 64-Bit Mode
Type 32-Bit 64-Bit
char 1 1
short 2 2
int 4 4
long 4 8
long long 8 8
float 4 4
double 8 8
pointer 4 8
According to ANSI, a bit field will have a type that is a qualified or unqualified
version of one of int, unsigned int, or signed int. Therefore, the ANSI mode
cannot change the type.
Bitfields in ANSI mode can only be signed int or unsigned int. In extended mode,
common mode, or k&r mode, non-integer bitfields are tolerated. When a
non-integer bitfield is tolerated, it means that any type other than int will be
converted to int.
The extended mode bitfields are updated to long types to admit 64-bit width in
64-bit mode. If a long type bitfield of length greater than 32-bits is used in 32-bit
extended mode, the following message is given:
1506-003 (S) Width of a bit-field of type "long" cannot exceed 32.
If a long type bitfield of length greater than 64-bits is used in 64-bit extended
mode, the following message is given:
60 AIX Version 4.3 Differences Guide