Each data type supported by XL C/C++ is aligned along byte boundaries according to platform-specific default alignment modes. On Linux®, the default alignment mode is linuxppc.
Each of the valid alignment modes is defined in Table 1, which provides the alignment value, in bytes, for scalar variables, for all data types. Where there are differences between 32-bit and 64-bit modes, these are indicated. Also, where there are differences between the first (scalar) member of an aggregate and subsequent members of the aggregate, these are indicated.
| Data type | Storage | Alignment setting | |
|---|---|---|---|
| linuxppc | bit_packed | ||
| _Bool (C), bool (C++) | 1 | 1 | 1 |
| char, signed char, unsigned char | 1 | 1 | 1 |
| wchar_t (32-bit mode) | 2 | 2 | 1 |
| wchar_t (64-bit mode) | 4 | 4 | 1 |
| int, unsigned int | 4 | 4 | 1 |
| short int, unsigned short int | 2 | 2 | 1 |
| long int, unsigned long int (32-bit mode) | 4 | 4 | 1 |
| long int, unsigned long int (64-bit mode) | 8 | 8 | 1 |
| long long | 8 | 8 | 1 |
| float | 4 | 4 | 1 |
| double | 8 | 8 | 1 |
| long double | 8 | 8 | 1 |
| long double with -qldbl128 | 16 | 16 | 1 |
| pointer (32-bit mode) | 4 | 4 | 1 |
| pointer (64-bit mode) | 8 | 8 | 1 |
| vector types | 16 | 16 | 1 |
Alignment of aggregates discusses the rules for the alignment of entire aggregates and provide examples of aggregate layouts. Alignment of bit fields discusses additional rules and considerations for the use and alignment of bit fields, and provides an example of bit-packed alignment.