Data Types

All of the data types used by various system interfaces are defined by the implementation. The following table describes some of these types. Other types referenced in the description of an interface, not mentioned here, can be found in the appropriate header for that interface.

Defined Type	Description
cc_t	Type used for terminal special characters.
clock_t	Arithmetic type used for processor times.
clockid_t	Used for clock ID type in some timer functions.
dev_t	Arithmetic type used for device numbers.
DIR	Type representing a directory stream.
div_t	Structure type returned by div() function.
FILE	A structure containing information about a file.
glob_t	Structure type used in pathname pattern matching.
fpos_t	Type containing all information needed to specify uniquely every position within a file.
gid_t	Arithmetic type used for group IDs.
iconv_t	Type used for conversion descriptors.
id_t	Arithmetic type used as a general identifier; can be used to contain at least the largest of a pid_t, uid_t or a gid_t.
ino_t	Arithmetic type used for file serial numbers.
key_t	Arithmetic type used for interprocess communication.
ldiv_t	Structure type returned by ldiv() function.
mode_t	Arithmetic type used for file attributes.
mqd_t	Used for message queue descriptors.
nfds_t	Integral type used for the number of file descriptors.
nlink_t	Arithmetic type used for link counts.
off_t	Signed Arithmetic type used for file sizes.
pid_t	Signed Arithmetic type used for process and process group IDs.
pthread_attr_t	Used to identify a thread attribute object.
pthread_cond_t	Used for condition variables.
pthread_condattr_t	Used to identify a condition attribute object.
pthread_key_t	Used for thread-specific data keys.
pthread_mutex_t	Used for mutexes.
pthread_mutexattr_t	Used to identify a mutex attribute object.
pthread_once_t	Used for dynamic package initialisation.
pthread_rwlock_t	Used for read-write locks.
pthread_rwlockattr_t	Used for read-write lock attributes.
pthread_t	Used to identify a thread.
ptrdiff_t	Signed integral type of the result of subtracting two pointers.
regex_t	Structure type used in regular expression matching.
regmatch_t	Structure type used in regular expression matching.
rlim_t	Unsigned arithmetic type used for limit values, to which objects of type int and off_t can be cast without loss of value.
sem_t	Type used in performing semaphore operations.
sig_atomic_t	Integral type of an object that can be accessed as an atomic entity, even in the presence of asynchronous interrupts.
sigset_t	Integral or structure type of an object used to represent sets of signals.
size_t	Unsigned integral type used for size of objects.
speed_t	Type used for terminal baud rates.
ssize_t	Arithmetic type used for a count of bytes or an error indication.
suseconds_t	A signed arithmetic type used for time in microseconds.
tcflag_t	Type used for terminal modes.
time_t	Arithmetic type used for time in seconds.
timer_t	Used for timer ID returned by timer_create().
uid_t	Arithmetic type used for user IDs.
useconds_t	Integral type used for time in microseconds.
va_list	Type used for traversing variable argument lists.
wchar_t	Integral type whose range of values can represent distinct codes for all members of the largest extended character set specified by the supported locales.
wctype_t	Scalar type which represents a character class descriptor.
wint_t	An integral type capable of storing any valid value of wchar_t, or
wordexp_t	Structure type used in word expansion.