Include: <aio.h>

struct	aiocb {
	int		aio_fildes;	/* File descriptor */
	off_t		aio_offset;	/* File offset */
	volatile void	*	aio_buf;	/* Location of buffer */
	size_t		aio_nbytes;	/* Length of transfer */
	int		aio_reqprio;	/* Request priority offset */
	struct sigevent		aio_sigevent;	/* Signal number and value */
	int		aio_lio_opcode;	/* Operation to be performed */
};

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)

Include: <time.h> or <sys/types.h> Alternatively, <sys/time.h>

Used for system time in clock ticks or CLOCKS_PER_SEC (defined in <time.h> 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)

Include: <sys/types.h> Alternatively, <time.h>

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)

Include: <sys/types.h> Alternatively, <sys/stat.h>

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)

Include: <stdlib.h>

typedef	struct {
	int		quot;	/* Quotient */
	int		rem;	/* Remainder */
} 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)

Include: <math.h>

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 <float.h>

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.

Include: <sys/select.h> Alternatively, <sys/time.h>

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)

Include: <fenv.h>

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)

Include: <fenv.h>

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)

Include: <stdio.h> Alternatively, <wchar.h>

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)

Include: <math.h>

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 <float.h>

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.

Include: <sys/types.h> Alternatively, <grp.h> <pwd.h> <signal.h> <stropts.h> <sys/ipc.h> <sys/stat.h> or <unistd.h>

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)

Include: <sys/types.h> Alternatively, <sys/resource.h>

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)

Include: <inttypes.h>

typedef	struct {
	intmax_t		quot;	/* Quotient */
	intmax_t		rem;	/* Remainder */
} 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)

Include: <stdint.h> Alternatively, <inttypes.h>

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.

Include: <stdint.h> Alternatively, <inttypes.h>

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 <inttypes.h> 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 <inttypes.h> 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.

Include: <stdint.h> Alternatively, <inttypes.h>

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 <inttypes.h> 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 <inttypes.h> 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.

Include: <locale.h>

struct	lconv {			/* Values in the "C" locale: */
	char	*	decimal_point;	/* "." */
	char	*	thousands_sep;	/* "" */
	char	*	grouping;	/* "" */
	char	*	mon_decimal_point;	/* "" */
	char	*	mon_thousands_sep;	/* "" */
	char	*	mon_grouping;	/* "" */
	char	*	positive_sign;	/* "" */
	char	*	negative_sign;	/* "" */
	char	*	currency_symbol;	/* "" */
	char		frac_digits;	/* CHAR_MAX */
	char		p_cs_precedes;	/* CHAR_MAX */
	char		n_cs_precedes;	/* CHAR_MAX */
	char		p_sep_by_space;	/* CHAR_MAX */
	char		n_sep_by_space;	/* CHAR_MAX */
	char		p_sign_posn;	/* CHAR_MAX */
	char		n_sign_posn;	/* CHAR_MAX */
	char	*	int_curr_symbol;	/* "" */
	char		int_frac_digits;	/* CHAR_MAX */
	char		int_p_cs_precedes;	/* CHAR_MAX */
	char		int_n_cs_precedes;	/* CHAR_MAX */
	char		int_p_sep_by_space;	/* CHAR_MAX */
	char		int_n_sep_by_space;	/* CHAR_MAX */
	char		int_p_sign_posn;	/* CHAR_MAX */
	char		int_n_sign_posn;	/* CHAR_MAX */
};

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)

Include: <stdlib.h>

typedef	struct {
	long		quot;	/* Quotient */
	long		rem;	/* Remainder */
} 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)

Include: <stdlib.h>

typedef	struct {
	long long		quot;	/* Quotient */
	long long		rem;	/* Remainder */
} 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)

Include: <sys/types.h>

Used for file sizes. It is a 64-bit signed integer type.

Conforming to: Present in glibc. It is not standardized by the C language standard nor POSIX.

Notes: The feature test macro _LARGEFILE64_SOURCE has to be defined for this type to be available.

See also: copy_file_range(2), readahead(2), sync_file_range(2), lseek64(3), feature_test_macros(7)

See also the off_t type in this page.

Include: <sys/types.h> Alternatively, <aio.h> <fcntl.h> <stdio.h> <sys/mman.h> <sys/stat.h.h> or <unistd.h>

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

Versions: <aio.h> and <stdio.h> 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)

See also the off64_t type in this page.

Include: <sys/types.h> Alternatively, <fcntl.h> <sched.h> <signal.h> <spawn.h> <sys/msg.h> <sys/sem.h> <sys/shm.h> <sys/wait.h> <termios.h> <time.h> <unistd.h> or <utmpx.h>

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),

Include: <stddef.h>

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.

Include: <regex.h>

typedef	struct {
	size_t		re_nsub;	/* Number of parenthesized subexpressions */
} 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)

Include: <regex.h>

typedef	struct {
	regoff_t		rm_so;	/* Byte offset from start of string to start of substring */
	regoff_t		rm_eo;	/* Byte offset from start of string of the first character after the end of substring */
} regmatch_t;

This is a structure type used in regular expression matching.

Conforming to: POSIX.1-2001 and later.

See also: regexec(3)

Include: <regex.h>

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.

Include: <signal.h> Alternatively, <aio.h> <mqueue.h> or <time.h>

struct	sigevent {
	int		sigev_notify;	/* Notification type */
	int		sigev_signo;	/* Signal number */
	union sigval		sigev_value;	/* Signal value */
	void	(*	sigev_notify_function)(union sigval);	/* Notification function */
	pthread_attr_t	*	sigev_notify_attributes;	/* Notification attributes */
};

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

Versions: <aio.h> and <time.h> 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.

Include: <signal.h> Alternatively, <sys/wait.h>

typedef	struct {
	int		si_signo;	/* Signal number */
	int		si_code;	/* Signal code */
	pid_t		si_pid;	/* Sending process ID */
	uid_t		si_uid;	/* Real user ID of sending process */
	void	*	si_addr;	/* Address of faulting instruction */
	int		si_status;	/* Exit value or signal */
	union sigval		si_value;	/* Signal value */
} 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)

Include: <signal.h> Alternatively, <spawn.h> or <sys/select.h>

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)

Include: <signal.h>

union	sigval {
	int		sigval_int;	/* Integer value */
	void	*	sigval_ptr;	/* Pointer value */
};

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.

Include: <stddef.h> or <sys/types.h> Alternatively, <aio.h> <glob.h> <grp.h> <iconv.h> <monetary.h> <mqueue.h> <ndbm.h> <pwd.h> <regex.h> <search.h> <signal.h> <stdio.h> <stdlib.h> <string.h> <strings.h> <sys/mman.h> <sys/msg.h> <sys/sem.h> <sys/shm.h> <sys/socket.h> <sys/uio.h> <time.h> <unistd.h> <wchar.h> or <wordexp.h>

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: <aio.h> <glob.h> <grp.h> <iconv.h> <mqueue.h> <pwd.h> <signal.h> and <sys/socket.h> 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.

Include: <sys/types.h> Alternatively, <aio.h> <monetary.h> <mqueue.h> <stdio.h> <sys/msg.h> <sys/socket.h> <sys/uio.h> or <unistd.h>

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.

Include: <sys/types.h> Alternatively, <sys/select.h> or <sys/time.h>

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.

Include: <time.h> or <sys/types.h> Alternatively, <sched.h> <sys/msg.h> <sys/select.h> <sys/sem.h> <sys/shm.h> <sys/stat.h> <sys/time.h> or <utime.h>

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

Versions: <sched.h> 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)

Include: <sys/types.h> Alternatively, <time.h>

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)

Include: <time.h> Alternatively, <aio.h> <mqueue.h> <sched.h> <signal.h> <sys/select.h> or <sys/stat.h>

struct	timespec {
	time_t		tv_sec;	/* Seconds */
	long		tv_nsec;	/* Nanoseconds */
};

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)

Include: <sys/time.h> Alternatively, <sys/resource.h> <sys/select.h> or <utmpx.h>

struct	timeval {
	time_t		tv_sec;	/* Seconds */
	suseconds_t		tv_usec;	/* Microseconds */
};

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)

Include: <sys/types.h> Alternatively, <pwd.h> <signal.h> <stropts.h> <sys/ipc.h> <sys/stat.h> or <unistd.h>

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)

Include: <stdint.h> Alternatively, <inttypes.h>

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.

Include: <stdint.h> Alternatively, <inttypes.h>

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 <inttypes.h> 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 <inttypes.h> 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.

Include: <stdint.h> Alternatively, <inttypes.h>

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 <inttypes.h> 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 <inttypes.h> 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.

Include: <stdarg>. Alternatively, <stdio.h> or <wchar.h>

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)

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.