<sys/types.h>

An application source file that includes <sys/types.h> makes the definitions of the programming model symbols, _LP64 and _ILP32, available through inclusion of <sys/isa_defs.h>. This header also contains a number of basic derived types that should be used whenever appropriate. In particular, the following are of special interest:

clock_t

The type clock_t represents the system times in clock ticks.

dev_t

The type dev_t is used for device numbers.

off_t

The type off_t is used for file sizes and offsets.

ptrdiff_t

The type ptrdiff_t is the signed integral type for the result of subtracting two pointers.

size_t

The type size_t is for the size, in bytes, of objects in memory.

ssize_t

The "signed size" type ssize_t is used by functions that return a count of bytes or an error indication.

time_t

The type time_t is used for time in seconds.

All of these types remain 32-bit quantities in the ILP32 compilation environment and grow to 64-bit quantities in the LP64 compilation environment.

The use of some of these types is explained in more detail later in this chapter under "Guidelines for Converting to LP64".