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TYPES(3) Library Functions Manual TYPES(3)

types
standard system data types

#include <sys/types.h>

The <sys/types.h> header contains the common data types used in the system. Although these are meant to be used within the kernel, most of the system data types are accessible also to user code. A companion header <sys/param.h>, typically used in the kernel, includes <sys/types.h> and provides additional types as well as other facilities (see param(3)).

The following standards-compliant system data types are defined:
Type Typical use Example
blkcnt_t file block counts stat(2)
blksize_t block sizes stat(2)
clock_t system clock ticks clock(3)
clockid_t clock IDs clock_settime(2)
dev_t device IDs devname(3)
fsblkcnt_t file system block counts -
fsfilcnt_t file system file counts -
gid_t group IDs getgid(2)
id_t general identifier pset(3)
ino_t file serial numbers fs(5)
key_t interprocess communication ftok(3)
mode_t file attributes stat(2)
nlink_t link counts stat(2)
off_t file sizes fseek(3)
pid_t process and process group IDs getpid(2)
size_t size of objects stddef(3)
ssize_t count of bytes write(2)
suseconds_t microseconds gettimeofday(2)
time_t time in seconds time(3)
timer_t timer IDs timer_create(2)
uid_t user IDs setuid(2)
useconds_t time in microseconds usleep(3)

In addition, when included in user applications, <sys/types.h> includes <pthread.h>, and thus it defines also the types used in the POSIX Threads Library, pthread(3).

Each described type may vary across machines and operating systems. Only the following properties are guaranteed by the IEEE Std 1003.1-2001 (“POSIX.1”) standard:

  1. The type ssize_t is capable of storing integer values at least in the range [-1, SSIZE_MAX].
  2. The type useconds_t is an unsigned integer capable of storing values at least in the range [0, 1000000].
  3. The type suseconds_t is a signed integer capable of storing values at least in the range [-1, 1000000].
  4. The time_t and clock_t types are either integers or real-floating types.
  5. The following types are integers: gid_t, id_t, mode_t, nlink_t, and uid_t.
  6. The following types are signed integers: blkcnt_t, blksize_t, off_t, pid_t, and ssize_t.
  7. The following types are unsigned integers: fsblkcnt_t, fsfilcnt_t, ino_t, and size_t.

In addition to the standard types, <sys/types.h> defines some data types specific to NetBSD. These are mostly used in the kernel. A portable implementation should not rely on these types to be available in other systems. Examples include:
Type Typical use Example
cpuid_t CPU IDs cpuset(3)
daddr_t disk address buffercache(9)
devmajor_t major device number getdevmajor(3)
lwp_t typedef of struct lwp kthread(9)
u_quad_t synonym for uint64_t strtouq(3)

It can be noted that the standard “C99 types” described in stdint(3) are preferred to the older fixed size integer types prefixed with an “u_” (in other words, uint32_t should be used instead of u_int32_t).

param(3), stdbool(3), stddef(3), stdint(3), stdlib(3), unistd(3)

The <sys/types.h> header conforms to IEEE Std 1003.1-2001 (“POSIX.1”) with respect to the described standard types.

The <sys/types.h> header first appeared in Version 7 AT&T UNIX. In the current form the header appeared in NetBSD 0.9.
April 10, 2011 NetBSD-7.0.1