The <sys/types.h> header 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.