SYSTEM_DATA_TYPES

NAME
DESCRIPTION
NOTES
EXAMPLES
SEE ALSO
COLOPHON

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NAME

system_data_types − overview of system data types

DESCRIPTION

aiocb

Include: .

struct aiocb {
int aio_fildes; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var File descriptor bodies/ usr/
off_t aio_offset; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var File offset bodies/ usr/
volatile void *aio_buf; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Location of buffer bodies/ usr/
size_t aio_nbytes; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Length of transfer bodies/ usr/
int aio_reqprio; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Request priority offset bodies/ usr/
struct sigevent aio_sigevent; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Signal number and value bodies/ usr/
int aio_lio_opcode;/* Operation to be performed bodies/ usr/
};

For further information about this structure, see aio(7).

Conforming to: POSIX.1-2001 and later.

See also: aio_cancel(3), aio_error(3), aio_fsync(3), aio_read(3), aio_return(3), aio_suspend(3), aio_write(3), lio_listio(3)

clock_t

Include: or . Alternatively, .

Used for system time in clock ticks or CLOCKS_PER_SEC (defined in ). According to POSIX, it shall be an integer type or a real-floating type.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: times(2), clock(3)

clockid_t

Include: . Alternatively, .

Used for clock ID type in the clock and timer functions. According to POSIX, it shall be defined as an arithmetic type.

Conforming to: POSIX.1-2001 and later.

See also: clock_adjtime(2), clock_getres(2), clock_nanosleep(2), timer_create(2), clock_getcpuclockid(3)

dev_t

Include: . Alternatively, .

Used for device IDs. According to POSIX, it shall be an integer type. For further details of this type, see makedev(3).

Conforming to: POSIX.1-2001 and later.

See also: mknod(2), stat(2)

div_t

Include: .

typedef struct {
int quot; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Quotient bodies/ usr/
int rem; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Remainder bodies/ usr/
} div_t;

It is the type of the value returned by the div(3) function.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: div(3)

double_t

Include: .

The implementation’s most efficient floating type at least as wide as double. Its type depends on the value of the macro FLT_EVAL_METHOD (defined in ):

	0		double_t is double.
	1		double_t is double.
	2		double_t is long double.

For other values of FLT_EVAL_METHOD, the type of double_t is implementation-defined.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: the float_t type in this page.

fd_set

Include: . Alternatively, .

A structure type that can represent a set of file descriptors. According to POSIX, the maximum number of file descriptors in an fd_set structure is the value of the macro FD_SETSIZE.

Conforming to: POSIX.1-2001 and later.

See also: select(2)

fenv_t

Include: .

This type represents the entire floating-point environment, including control modes and status flags; for further details, see fenv(3).

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: fenv(3)

fexcept_t

Include: .

This type represents the floating-point status flags collectively; for further details see fenv(3).

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: fenv(3)

FILE

Include: . Alternatively, .

An object type used for streams.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: fclose(3), flockfile(3), fopen(3), fprintf(3), fread(3), fscanf(3), stdin(3), stdio(3)

float_t

Include: .

The implementation’s most efficient floating type at least as wide as float. Its type depends on the value of the macro FLT_EVAL_METHOD (defined in ):

	0		float_t is float.
	1		float_t is double.
	2		float_t is long double.

For other values of FLT_EVAL_METHOD, the type of float_t is implementation-defined.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: the double_t type in this page.

gid_t

Include: . Alternatively, , , , , , , or .

A type used to hold group IDs. According to POSIX, this shall be an integer type.

Conforming to: POSIX.1-2001 and later.

See also: chown(2), getgid(2), getegid(2), getgroups(2), getresgid(2), getgrnam(2), credentials(7)

id_t

Include: . Alternatively, .

A type used to hold a general identifier. According to POSIX, this shall be an integer type that can be used to contain a pid_t, uid_t, or gid_t.

Conforming to: POSIX.1-2001 and later.

See also: getpriority(2), waitid(2)

imaxdiv_t

Include: .

typedef struct {
intmax_t quot; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Quotient bodies/ usr/
intmax_t rem; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Remainder bodies/ usr/
} imaxdiv_t;

It is the type of the value returned by the imaxdiv(3) function.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: imaxdiv(3)

intmax_t

Include: . Alternatively, .

A signed integer type capable of representing any value of any signed integer type supported by the implementation. According to the C language standard, it shall be capable of storing values in the range [INTMAX_MIN, INTMAX_MAX].

The macro INTMAX_C() expands its argument to an integer constant of type intmax_t.

The length modifier for intmax_t for the printf(3) and the scanf(3) families of functions is j; resulting commonly in %jd or %ji for printing intmax_t values.

Conforming to: C99 and later; POSIX.1-2001 and later.

Bugs: intmax_t is not large enough to represent values of type __int128 in implementations where __int128 is defined and long long is less than 128 bits wide.

See also: the uintmax_t type in this page.

intN_t

Include: . Alternatively, .

int8_t, int16_t, int32_t, int64_t

A signed integer type of a fixed width of exactly N bits, N being the value specified in its type name. According to the C language standard, they shall be capable of storing values in the range [INTN_MIN, INTN_MAX], substituting N by the appropriate number.

According to POSIX, int8_t, int16_t, and int32_t are required; int64_t is only required in implementations that provide integer types with width 64; and all other types of this form are optional.

The length modifiers for the intN_t types for the printf(3) family of functions are expanded by macros of the forms PRIdN and PRIiN (defined in ); resulting for example in %”PRId64″ or %”PRIi64″ for printing int64_t values. The length modifiers for the intN_t types for the scanf(3) family of functions are expanded by macros of the forms SCNdN and SCNiN, (defined in ); resulting for example in %”SCNd8″ or %”SCNi8″ for scanning int8_t values.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: the intmax_t, uintN_t, and uintmax_t types in this page.

intptr_t

Include: . Alternatively, .

A signed integer type such that any valid (void *) value can be converted to this type and back. According to the C language standard, it shall be capable of storing values in the range [INTPTR_MIN, INTPTR_MAX].

The length modifier for intptr_t for the printf(3) family of functions is expanded by the macros PRIdPTR and PRIiPTR (defined in ); resulting commonly in %”PRIdPTR” or %”PRIiPTR” for printing intptr_t values. The length modifier for intptr_t for the scanf(3) family of functions is expanded by the macros SCNdPTR and SCNiPTR, (defined in ); resulting commonly in %”SCNdPTR” or %”SCNiPTR” for scanning intptr_t values.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: the uintptr_t and void * types in this page.

lconv

Include: .

struct lconv { /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Values in the “C” locale: bodies/ usr/
char *decimal_point; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var “.” bodies/ usr/
char *thousands_sep; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var “” bodies/ usr/
char *grouping; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var “” bodies/ usr/
char *mon_decimal_point; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var “” bodies/ usr/
char *mon_thousands_sep; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var “” bodies/ usr/
char *mon_grouping; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var “” bodies/ usr/
char *positive_sign; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var “” bodies/ usr/
char *negative_sign; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var “” bodies/ usr/
char *currency_symbol; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var “” bodies/ usr/
char frac_digits; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char p_cs_precedes; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char n_cs_precedes; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char p_sep_by_space; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char n_sep_by_space; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char p_sign_posn; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char n_sign_posn; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char *int_curr_symbol; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var “” bodies/ usr/
char int_frac_digits; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char int_p_cs_precedes; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char int_n_cs_precedes; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char int_p_sep_by_space; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char int_n_sep_by_space; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char int_p_sign_posn; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
char int_n_sign_posn; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var CHAR_MAX bodies/ usr/
};

Contains members related to the formatting of numeric values. In the “C” locale, its members have the values shown in the comments above.

Conforming to: C11 and later; POSIX.1-2001 and later.

See also: setlocale(3), localeconv(3), charsets(5), locale(7)

ldiv_t

Include: .

typedef struct {
long quot; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Quotient bodies/ usr/
long rem; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Remainder bodies/ usr/
} ldiv_t;

It is the type of the value returned by the ldiv(3) function.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: ldiv(3)

lldiv_t

Include: .

typedef struct {
long long quot; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Quotient bodies/ usr/
long long rem; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Remainder bodies/ usr/
} lldiv_t;

It is the type of the value returned by the lldiv(3) function.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: lldiv(3)

off_t

Include: . Alternatively, , , , , , or .

Used for file sizes. According to POSIX, this shall be a signed integer type.

Versions: and define off_t since POSIX.1-2008.

Conforming to: POSIX.1-2001 and later.

Notes: On some architectures, the width of this type can be controlled with the feature test macro _FILE_OFFSET_BITS.

See also: lseek(2), mmap(2), posix_fadvise(2), pread(2), truncate(2), fseeko(3), lockf(3), posix_fallocate(3), feature_test_macros(7)

pid_t

Include: . Alternatively, , , , , , , , , , , , or .

This type is used for storing process IDs, process group IDs, and session IDs. According to POSIX, it shall be a signed integer type, and the implementation shall support one or more programming environments where the width of pid_t is no greater than the width of the type long.

Conforming to: POSIX.1-2001 and later.

See also: fork(2), getpid(2), getppid(2), getsid(2), gettid(2), getpgid(2), kill(2), pidfd_open(2), sched_setscheduler(2), waitpid(2), sigqueue(3), credentials(7),

ptrdiff_t

Include: .

Used for a count of elements, and array indices. It is the result of subtracting two pointers. According to the C language standard, it shall be a signed integer type capable of storing values in the range [PTRDIFF_MIN, PTRDIFF_MAX].

The length modifier for ptrdiff_t for the printf(3) and the scanf(3) families of functions is t; resulting commonly in %td or %ti for printing ptrdiff_t values.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: the size_t and ssize_t types in this page.

regex_t

Include: .

typedef struct {
size_t re_nsub; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Number of parenthesized subexpressions. bodies/ usr/
} regex_t;

This is a structure type used in regular expression matching. It holds a compiled regular expression, compiled with regcomp(3).

Conforming to: POSIX.1-2001 and later.

See also: regex(3)

regmatch_t

Include: .

typedef struct {
regoff_t rm_so; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Byte offset from start of string
to start of substring bodies/ usr/
regoff_t rm_eo; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Byte offset from start of string of
the first character after the end of
substring bodies/ usr/
} regmatch_t;

This is a structure type used in regular expression matching.

Conforming to: POSIX.1-2001 and later.

See also: regexec(3)

regoff_t

Include: .

According to POSIX, it shall be a signed integer type capable of storing the largest value that can be stored in either a ptrdiff_t type or a ssize_t type.

Versions: Prior to POSIX.1-2008, the type was capable of storing the largest value that can be stored in either an off_t type or a ssize_t type.

Conforming to: POSIX.1-2001 and later.

See also: the regmatch_t structure and the ptrdiff_t and ssize_t types in this page.

sigevent

Include: . Alternatively, , , or .

struct sigevent {
int sigev_notify; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Notification type bodies/ usr/
int sigev_signo; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Signal number bodies/ usr/
union sigval sigev_value; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Signal value bodies/ usr/
void (*sigev_notify_function)(union sigval);
/bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Notification function bodies/ usr/
pthread_attr_t *sigev_notify_attributes;
/bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Notification attributes bodies/ usr/
};

For further details about this type, see sigevent(7).

Versions: and define sigevent since POSIX.1-2008.

Conforming to: POSIX.1-2001 and later.

See also: timer_create(2), getaddrinfo_a(3), lio_listio(3), mq_notify(3)

See also the aiocb structure in this page.

siginfo_t

Include: . Alternatively, .

typedef struct {
int si_signo; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Signal number bodies/ usr/
int si_code; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Signal code bodies/ usr/
pid_t si_pid; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Sending process ID bodies/ usr/
uid_t si_uid; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Real user ID of sending process bodies/ usr/
void *si_addr; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Address of faulting instruction bodies/ usr/
int si_status; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Exit value or signal bodies/ usr/
union sigval si_value; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Signal value bodies/ usr/
} siginfo_t;

Information associated with a signal. For further details on this structure (including additional, Linux-specific fields), see sigaction(2).

Conforming to: POSIX.1-2001 and later.

See also: pidfd_send_signal(2), rt_sigqueueinfo(2), sigaction(2), sigwaitinfo(2), psiginfo(3)

sigset_t

Include: . Alternatively, , or .

This is a type that represents a set of signals. According to POSIX, this shall be an integer or structure type.

Conforming to: POSIX.1-2001 and later.

See also: epoll_pwait(2), ppoll(2), pselect(2), sigaction(2), signalfd(2), sigpending(2), sigprocmask(2), sigsuspend(2), sigwaitinfo(2), signal(7)

sigval

Include: .

union sigval {
int sigval_int; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Integer value bodies/ usr/
void *sigval_ptr; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Pointer value bodies/ usr/
};

Data passed with a signal.

Conforming to: POSIX.1-2001 and later.

See also: pthread_sigqueue(3), sigqueue(3), sigevent(7)

See also the sigevent structure and the siginfo_t type in this page.

size_t

Include: or . Alternatively, , , , , , , , , , , , , , , , , , , , , , , , , or .

Used for a count of bytes. It is the result of the sizeof operator. According to the C language standard, it shall be an unsigned integer type capable of storing values in the range [0, SIZE_MAX]. According to POSIX, the implementation shall support one or more programming environments where the width of size_t is no greater than the width of the type long.

The length modifier for size_t for the printf(3) and the scanf(3) families of functions is z; resulting commonly in %zu or %zx for printing size_t values.

Versions: , , , , , , , and define size_t since POSIX.1-2008.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: read(2), write(2), fread(3), fwrite(3), memcmp(3), memcpy(3), memset(3), offsetof(3)

See also the ptrdiff_t and ssize_t types in this page.

ssize_t

Include: . Alternatively, , , , , , , , or .

Used for a count of bytes or an error indication. According to POSIX, it shall be a signed integer type capable of storing values at least in the range [-1, SSIZE_MAX], and the implementation shall support one or more programming environments where the width of ssize_t is no greater than the width of the type long.

Glibc and most other implementations provide a length modifier for ssize_t for the printf(3) and the scanf(3) families of functions, which is z; resulting commonly in %zd or %zi for printing ssize_t values. Although z works for ssize_t on most implementations, portable POSIX programs should avoid using it—for example, by converting the value to intmax_t and using its length modifier (j).

Conforming to: POSIX.1-2001 and later.

See also: read(2), readlink(2), readv(2), recv(2), send(2), write(2)

See also the ptrdiff_t and size_t types in this page.

suseconds_t

Include: . Alternatively, , or .

Used for time in microseconds. According to POSIX, it shall be a signed integer type capable of storing values at least in the range [-1, 1000000], and the implementation shall support one or more programming environments where the width of suseconds_t is no greater than the width of the type long.

Conforming to: POSIX.1-2001 and later.

See also: the timeval structure in this page.

time_t

Include: or . Alternatively, , , , , , , , or .

Used for time in seconds. According to POSIX, it shall be an integer type.

Versions: defines time_t since POSIX.1-2008.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: stime(2), time(2), ctime(3), difftime(3)

timer_t

Include: . Alternatively, .

Used for timer ID returned by timer_create(2). According to POSIX, there are no defined comparison or assignment operators for this type.

Conforming to: POSIX.1-2001 and later.

See also: timer_create(2), timer_delete(2), timer_getoverrun(2), timer_settime(2)

timespec

Include: . Alternatively, , , , , , or .

struct timespec {
time_t tv_sec; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Seconds bodies/ usr/
long tv_nsec; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Nanoseconds bodies/ usr/
};

Describes times in seconds and nanoseconds.

Conforming to: C11 and later; POSIX.1-2001 and later.

See also: clock_gettime(2), clock_nanosleep(2), nanosleep(2), timerfd_gettime(2), timer_gettime(2)

timeval

Include: . Alternatively, , , or .

struct timeval {
time_t tv_sec; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Seconds bodies/ usr/
suseconds_t tv_usec; /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Microseconds bodies/ usr/
};

Describes times in seconds and microseconds.

Conforming to: POSIX.1-2001 and later.

See also: gettimeofday(2), select(2), utimes(2), adjtime(3), futimes(3), timeradd(3)

uid_t

Include: . Alternatively, , , , , , or .

A type used to hold user IDs. According to POSIX, this shall be an integer type.

Conforming to: POSIX.1-2001 and later.

See also: chown(2), getuid(2), geteuid(2), getresuid(2), getpwnam(2), credentials(7)

uintmax_t

Include: . Alternatively, .

An unsigned integer type capable of representing any value of any unsigned integer type supported by the implementation. According to the C language standard, it shall be capable of storing values in the range [0, UINTMAX_MAX].

The macro UINTMAX_C() expands its argument to an integer constant of type uintmax_t.

The length modifier for uintmax_t for the printf(3) and the scanf(3) families of functions is j; resulting commonly in %ju or %jx for printing uintmax_t values.

Conforming to: C99 and later; POSIX.1-2001 and later.

Bugs: uintmax_t is not large enough to represent values of type unsigned __int128 in implementations where unsigned __int128 is defined and unsigned long long is less than 128 bits wide.

See also: the intmax_t type in this page.

uintN_t

Include: . Alternatively, .

uint8_t, uint16_t, uint32_t, uint64_t

An unsigned integer type of a fixed width of exactly N bits, N being the value specified in its type name. According to the C language standard, they shall be capable of storing values in the range [0, UINTN_MAX], substituting N by the appropriate number.

According to POSIX, uint8_t, uint16_t, and uint32_t are required; uint64_t is only required in implementations that provide integer types with width 64; and all other types of this form are optional.

The length modifiers for the uintN_t types for the printf(3) family of functions are expanded by macros of the forms PRIuN, PRIoN, PRIxN, and PRIXN (defined in ); resulting for example in %”PRIu32″ or %”PRIx32″ for printing uint32_t values. The length modifiers for the uintN_t types for the scanf(3) family of functions are expanded by macros of the forms SCNuN, SCNoN, SCNxN, and SCNXN (defined in ); resulting for example in %”SCNu16″ or %”SCNx16″ for scanning uint16_t values.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: the intmax_t, intN_t, and uintmax_t types in this page.

uintptr_t

Include: . Alternatively, .

An unsigned integer type such that any valid (void *) value can be converted to this type and back. According to the C language standard, it shall be capable of storing values in the range [0, UINTPTR_MAX].

The length modifier for uintptr_t for the printf(3) family of functions is expanded by the macros PRIuPTR, PRIoPTR, PRIxPTR, and PRIXPTR (defined in ); resulting commonly in %”PRIuPTR” or %”PRIxPTR” for printing uintptr_t values. The length modifier for uintptr_t for the scanf(3) family of functions is expanded by the macros SCNuPTR, SCNoPTR, SCNxPTR, and SCNXPTR (defined in ); resulting commonly in %”SCNuPTR” or %”SCNxPTR” for scanning uintptr_t values.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: the intptr_t and void * types in this page.

va_list

Include: . Alternatively, , or .

Used by functions with a varying number of arguments of varying types. The function must declare an object of type va_list which is used by the macros va_start(3), va_arg(3), va_copy(3), and va_end(3) to traverse the list of arguments.

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: va_start(3), va_arg(3), va_copy(3), va_end(3)

void *

According to the C language standard, a pointer to any object type may be converted to a pointer to void and back. POSIX further requires that any pointer, including pointers to functions, may be converted to a pointer to void and back.

Conversions from and to any other pointer type are done implicitly, not requiring casts at all. Note that this feature prevents any kind of type checking: the programmer should be careful not to convert a void * value to a type incompatible to that of the underlying data, because that would result in undefined behavior.

This type is useful in function parameters and return value to allow passing values of any type. The function will typically use some mechanism to know the real type of the data being passed via a pointer to void.

A value of this type can’t be dereferenced, as it would give a value of type void, which is not possible. Likewise, pointer arithmetic is not possible with this type. However, in GNU C, pointer arithmetic is allowed as an extension to the standard; this is done by treating the size of a void or of a function as 1. A consequence of this is that sizeof is also allowed on void and on function types, and returns 1.

The conversion specifier for void * for the printf(3) and the scanf(3) families of functions is p.

Versions: The POSIX requirement about compatibility between void * and function pointers was added in POSIX.1-2008 Technical Corrigendum 1 (2013).

Conforming to: C99 and later; POSIX.1-2001 and later.

See also: malloc(3), memcmp(3), memcpy(3), memset(3)

See also the intptr_t and uintptr_t types in this page.

NOTES

The structures described in this manual page shall contain, at least, the members shown in their definition, in no particular order.

Most of the integer types described in this page don’t have a corresponding length modifier for the printf(3) and the scanf(3) families of functions. To print a value of an integer type that doesn’t have a length modifier, it should be converted to intmax_t or uintmax_t by an explicit cast. To scan into a variable of an integer type that doesn’t have a length modifier, an intermediate temporary variable of type intmax_t or uintmax_t should be used. When copying from the temporary variable to the destination variable, the value could overflow. If the type has upper and lower limits, the user should check that the value is within those limits, before actually copying the value. The example below shows how these conversions should be done.

Conventions used in this page
In “Conforming to” we only concern ourselves with C99 and later and POSIX.1-2001 and later. Some types may be specified in earlier versions of one of these standards, but in the interests of simplicity we omit details from earlier standards.

In “Include”, we first note the “primary” header(s) that define the type according to either the C or POSIX.1 standards. Under “Alternatively”, we note additional headers that the standards specify shall define the type.

EXAMPLES

The program shown below scans from a string and prints a value stored in a variable of an integer type that doesn’t have a length modifier. The appropriate conversions from and to intmax_t, and the appropriate range checks, are used as explained in the notes section above.

#include
#include
#include
#include

int
main (void)
{
static const char *const str = “500000 us in half a second”;
suseconds_t us;
intmax_t tmp;

/* Scan the number from the string into the temporary variable */

sscanf(str, “%jd”, &tmp);

/* Check that the value is within the valid range of suseconds_t */

if (tmp < −1 || tmp > 1000000) {
fprintf(stderr, “Scanned value outside valid range!n”);
exit(EXIT_FAILURE);
}

/* Copy the value to the suseconds_t variable ‘us’ */

us = tmp;

/* Even though suseconds_t can hold the value −1, this isn’t
a sensible number of microseconds */

if (us < 0) {
fprintf(stderr, “Scanned value shouldn’t be negative!n”);
exit(EXIT_FAILURE);
}

/* Print the value */

printf(“There are %jd microseconds in half a second.n”,
(intmax_t) us);

exit(EXIT_SUCCESS);
}

SEE ALSO

feature_test_macros(7), standards(7)

COLOPHON

This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man−pages/.

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