man-pages/man7/system_data_types.7

.\" Copyright (c) 2020 by Alejandro Colomar <colomar.6.4.3@gmail.com>
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.\"
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.\"
.TH SYSTEM_DATA_TYPES 7 2020-09-13 "Linux" "Linux Programmer's Manual"
.SH NAME
system_data_types \- overview of system data types
.SH DESCRIPTION
.\" Layout:
.\"	A list of type names (the struct/union keyword will be omitted).
.\"	Each entry will have the following parts:
.\"		* Include
.\"			The headers will be in the following order:
.\"			1) The main header that shall define the type
.\"			   according to the C Standard,
.\"			   and
.\"			   the main header that shall define the type
.\"			   according to POSIX,
.\"			   in alphabetical order.
.\"			;
.\"			2) All other headers that shall define the type
.\"			   as described in the previous header(s)
.\"			   according to the C Standard or POSIX,
.\"			   in alphabetical order.
.\"			*) All headers that define the type
.\"			   *if* the type is not defined by C nor POSIX,
.\"			   in alphabetical order.
.\"
.\"		* Definition (no "Definition" header)
.\"			Only struct/union types will have definition;
.\"			typedefs will remain opaque.
.\"
.\"		* Description (no "Description" header)
.\"			A few lines describing the type.
.\"
.\"		* Conforming to
.\"			Format: CXY and later; POSIX.1-XXXX and later.
.\"			Forget about pre-C99 C standards (i.e., C89/C90)
.\"
.\"		* Notes (optional)
.\"
.\"		* See also
.\"------------------------------------- aiocb ------------------------/
.TP
.I aiocb
.IP
Include:
.IR <aio.h> .
.IP
.EX
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 */
};
.EE
.IP
For further information about this structure, see
.BR aio (7).
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR aio_cancel (3),
.BR aio_error (3),
.BR aio_fsync (3),
.BR aio_read (3),
.BR aio_return (3),
.BR aio_suspend (3),
.BR aio_write (3),
.BR lio_listio (3)
.\"------------------------------------- div_t ------------------------/
.TP
.I div_t
.IP
Include:
.IR <stdlib.h> .
.IP
.EX
typedef struct {
    int quot; /* Quotient */
    int rem;  /* Remainder */
} div_t;
.EE
.IP
It is the type of the value returned by the
.BR div (3)
function.
.IP
Conforming to: C99 and later; POSIX.1-2001 and later.
.IP
See also:
.BR div (3)
.\"------------------------------------- fenv_t -----------------------/
.TP
.I fenv_t
.IP
Include:
.IR <fenv.h> .
.IP
This type represents the entire floating-point environment,
including control modes and status flags; for further details, see
.BR fenv (3).
.IP
Conforming to: C99 and later; POSIX.1-2001 and later.
.IP
See also:
.BR fenv (3)
.\"------------------------------------- fexcept_t --------------------/
.TP
.I fexcept_t
.IP
Include:
.IR <fenv.h> .
.IP
This type represents the floating-point status flags collectively;
for further details see
.BR fenv (3).
.IP
Conforming to: C99 and later; POSIX.1-2001 and later.
.IP
See also:
.BR fenv (3)
.\"------------------------------------- gid_t ------------------------/
.TP
.I gid_t
.IP
Include:
.IR <sys/types.h> ;
or
.I <grp.h>
or
.I <pwd.h>
or
.I <signal.h>
or
.I <stropts.h>
or
.I <sys/ipc.h>
or
.I <sys/stat.h>
or
.IR <unistd.h> .
.IP
A type used to hold group IDs.
According to POSIX,
this shall be an integer type.
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR chown (2),
.BR getgid (2),
.BR getegid (2),
.BR getgroups (2),
.BR getresgid (2),
.BR getgrnam (2),
.BR credentials (7)
.\"------------------------------------- id_t -------------------------/
.TP
.I id_t
.IP
Include:
.IR <sys/types.h> ;
or
.IR <sys/resource.h> .
.IP
A type used to hold a general identifier.
According to POSIX,
this shall be an integer type that can be used to contain a
.IR pid_t ,
.IR uid_t ,
or
.IR gid_t .
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR getpriority (2),
.BR waitid (2)
.\"------------------------------------- imaxdiv_t --------------------/
.TP
.I imaxdiv_t
.IP
Include:
.IR <inttypes.h> .
.IP
.EX
typedef struct {
    intmax_t    quot; /* Quotient */
    intmax_t    rem;  /* Remainder */
} imaxdiv_t;
.EE
.IP
It is the type of the value returned by the
.BR imaxdiv (3)
function.
.IP
Conforming to: C99 and later; POSIX.1-2001 and later.
.IP
See also:
.BR imaxdiv (3)
.\"------------------------------------- lconv ------------------------/
.TP
.I lconv
.IP
Include:
.IR <locale.h> .
.IP
.EX
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 */
};
.EE
.IP
Contains members related to the formatting of numeric values.
In the "C" locale, its members have the values
shown in the comments above.
.IP
Conforming to: C11 and later; POSIX.1-2001 and later.
.IP
See also:
.BR setlocale (3),
.BR localeconv (3),
.BR charsets (5),
.BR locale (7)
.\"------------------------------------- ldiv_t -----------------------/
.TP
.I ldiv_t
.IP
Include:
.IR <stdlib.h> .
.IP
.EX
typedef struct {
    long    quot; /* Quotient */
    long    rem;  /* Remainder */
} ldiv_t;
.EE
.IP
It is the type of the value returned by the
.BR ldiv (3)
function.
.IP
Conforming to: C99 and later; POSIX.1-2001 and later.
.IP
See also:
.BR ldiv (3)
.\"------------------------------------- lldiv_t ----------------------/
.TP
.I lldiv_t
.IP
Include:
.IR <stdlib.h> .
.IP
.EX
typedef struct {
    long long   quot; /* Quotient */
    long long   rem;  /* Remainder */
} lldiv_t;
.EE
.IP
It is the type of the value returned by the
.BR lldiv (3)
function.
.IP
Conforming to: C99 and later; POSIX.1-2001 and later.
.IP
See also:
.BR lldiv (3)
.\"------------------------------------- pid_t ------------------------/
.TP
.I pid_t
.IP
Include
.IR <sys/types.h> ;
or
.I <fcntl.h>
or
.I <sched.h>
or
.I <signal.h>
or
.I <spawn.h>
or
.I <sys/msg.h>
or
.I <sys/sem.h>
or
.I <sys/shm.h>
or
.I <sys/wait.h>
or
.I <termios.h>
or
.I <time.h>
or
.I <unistd.h>
or
.IR <utmpx.h> .
.IP
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
.I pid_t
is no greater than the width of the type
.IR long .
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR fork (2),
.BR getpid (2),
.BR getppid (2),
.BR getsid (2),
.BR gettid (2),
.BR getpgid (2),
.BR kill (2),
.BR pidfd_open (2),
.BR sched_setscheduler (2),
.BR waitpid (2),
.BR sigqueue (3),
.BR credentials (7),
.\"------------------------------------- ptrdiff_t --------------------/
.TP
.I ptrdiff_t
.IP
Include:
.IR <stddef.h> .
.IP
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
.RB [ PTRDIFF_MIN ,
.BR PTRDIFF_MAX ].
.IP
The length modifier for
.I ptrdiff_t
for the
.BR printf (3)
and the
.BR scanf (3)
families of functions is
.BR t ;
resulting commonly in
.B %td
or
.B %ti
for printing
.I ptrdiff_t
values.
.IP
Conforming to: C99 and later; POSIX.1-2001 and later.
.IP
See also the
.I size_t
and
.I ssize_t
types in this page.
.\"------------------------------------- regmatch_t -------------------/
.TP
.I regmatch_t
.IP
Include:
.IR <regex.h> .
.IP
.EX
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;
.EE
.IP
This is a structure type used in regular expression matching.
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR regexec (3)
.\"------------------------------------- regoff_t ---------------------/
.TP
.I regoff_t
.IP
Include:
.IR <regex.h> .
.IP
According to POSIX, it shall be a signed integer type
capable of storing the largest value that can be stored in either a
.I ptrdiff_t
type or a
.I ssize_t
type.
.IP
Conforming to: POSIX.1-2001 and later.
.IP
Notes: Prior to POSIX.1-2008, the type was capable of storing
the largest value that can be stored in either an
.I off_t
type or a
.I ssize_t
type.
.IP
See also the
.I regmatch_t
structure and the
.I ptrdiff_t
and
.I ssize_t
types in this page.
.\"------------------------------------- sigevent ---------------------/
.TP
.I sigevent
.IP
Include:
.IR <signal.h> ;
or
.I <aio.h>
or
.I <mqueue.h>
or
.IR <time.h> .
.IP
.EX
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 */
};
.EE
.IP
For further details about this type, see
.BR sigevent (7).
.IP
Conforming to: POSIX.1-2001 and later.
.IP
Notes:
.I <aio.h>
and
.I <time.h>
define
.I sigevent
since POSIX.1-2008.
.IP
See also:
.BR timer_create (2),
.BR getaddrinfo_a (3),
.BR lio_listio (3),
.BR mq_notify (3)
.IP
See also the
.I aiocb
structure in this page.
.\"------------------------------------- siginfo_t --------------------/
.TP
.I siginfo_t
.IP
Include:
.IR <signal.h> ;
or
.IR <sys/wait.h> .
.IP
.EX
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;
.EE
.IP
Information associated with a signal.
For further details on this structure
(including additional, Linux-specific fields), see
.BR sigaction (2).
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR pidfd_send_signal (2),
.BR rt_sigqueueinfo (2),
.BR sigaction (2),
.BR sigwaitinfo (2),
.BR psiginfo (3)
.\"------------------------------------- sigset_t ---------------------/
.TP
.I sigset_t
.IP
Include:
.IR <signal.h> ;
or
.I <spawn.h>
or
.IR <sys/select.h> .
.IP
This is a type that represents a set of signals.
According to POSIX, this shall be an integer or structure type.
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR epoll_pwait (2),
.BR ppoll (2),
.BR pselect (2),
.BR sigaction (2),
.BR signalfd (2),
.BR sigpending (2),
.BR sigprocmask (2),
.BR sigsuspend (2),
.BR sigwaitinfo (2),
.BR signal (7)
.\"------------------------------------- sigval -----------------------/
.TP
.I sigval
.IP
Include:
.IR <signal.h> .
.IP
.EX
union sigval {
    int     sigval_int; /* Integer value */
    void   *sigval_ptr; /* Pointer value */
};
.EE
.IP
Data passed with a signal.
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR pthread_sigqueue (3),
.BR sigqueue (3),
.BR sigevent (7)
.IP
See also the
.I sigevent
structure
and the
.I siginfo_t
type
in this page.
.\"------------------------------------- size_t -----------------------/
.TP
.I size_t
.IP
Include:
.I <stddef.h>
or
.IR <sys/types.h> ;
or
.I <aio.h>
or
.I <glob.h>
or
.I <grp.h>
or
.I <iconv.h>
or
.I <monetary.h>
or
.I <mqueue.h>
or
.I <ndbm.h>
or
.I <pwd.h>
or
.I <regex.h>
or
.I <search.h>
or
.I <signal.h>
or
.I <stdio.h>
or
.I <stdlib.h>
or
.I <string.h>
or
.I <strings.h>
or
.I <sys/mman.h>
or
.I <sys/msg.h>
or
.I <sys/sem.h>
or
.I <sys/shm.h>
or
.I <sys/socket.h>
or
.I <sys/uio.h>
or
.I <time.h>
or
.I <unistd.h>
or
.I <wchar.h>
or
.IR <wordexp.h> .
.IP
Used for a count of bytes.  It is the result of the
.I sizeof
operator.
According to the C language standard,
it shall be an unsigned integer type
capable of storing values in the range [0,
.BR SIZE_MAX ].
According to POSIX,
the implementation shall support one or more programming environments
where the width of
.I size_t
is no greater than the width of the type
.IR long .
.IP
The length modifier for
.I size_t
for the
.BR printf (3)
and the
.BR scanf (3)
families of functions is
.BR z ;
resulting commonly in
.B %zu
or
.B %zx
for printing
.I size_t
values.
.IP
Conforming to: C99 and later; POSIX.1-2001 and later.
.IP
Notes:
.IR <aio.h> ,
.IR <glob.h> ,
.IR <grp.h> ,
.IR <iconv.h> ,
.IR <mqueue.h> ,
.IR <pwd.h> ,
.I <signal.h>
and
.I <sys/socket.h>
define
.I size_t
since POSIX.1-2008.
.IP
See also:
.BR read (2),
.BR write (2),
.BR memcmp (3),
.BR fread (3),
.BR fwrite (3),
.BR memcmp (3),
.BR memcpy (3),
.BR memset (3),
.BR offsetof (3)
.IP
See also the
.I ptrdiff_t
and
.I ssize_t
types in this page.
.\"------------------------------------- ssize_t ----------------------/
.TP
.I ssize_t
.IP
Include:
.IR <sys/types.h> ;
or
.I <aio.h>
or
.I <monetary.h>
or
.I <mqueue.h>
or
.I <stdio.h>
or
.I <sys/msg.h>
or
.I <sys/socket.h>
or
.I <sys/uio.h>
or
.IR <unistd.h> .
.IP
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,
.BR SSIZE_MAX ],
and the implementation shall support one or more programming environments
where the width of
.I ssize_t
is no greater than the width of the type
.IR long .
.IP
Glibc and most other implementations provide a length modifier for
.I ssize_t
for the
.BR printf (3)
and the
.BR scanf (3)
families of functions, which is
.BR z ;
resulting commonly in
.B %zd
or
.B %zi
for printing
.I ssize_t
values.
Although
.B z
works for
.I ssize_t
on most implementations,
portable POSIX programs should avoid using it\(emfor example,
by converting the value to
.I intmax_t
and using its length modifier
.RB ( j ).
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR read (2),
.BR readlink (2),
.BR readv (2),
.BR recv (2),
.BR send (2),
.BR write (2)
.IP
See also the
.I ptrdiff_t
and
.I size_t
types in this page.
.\"------------------------------------- suseconds_t ------------------/
.TP
.I suseconds_t
.IP
Include:
.IR <sys/types.h> ;
or
.I <sys/select.h>
or
.IR <sys/time.h> .
.IP
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
.I suseconds_t
is no greater than the width of the type
.IR long .
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also the
.I timeval
structure in this page.
.\"------------------------------------- time_t -----------------------/
.TP
.I time_t
.IP
Include:
.I <sys/types.h>
or
.IR <time.h> ;
or
.I <sched.h>
or
.I <sys/msg.h>
or
.I <sys/select.h>
or
.I <sys/sem.h>
or
.I <sys/shm.h>
or
.I <sys/stat.h>
or
.I <sys/time.h>
or
.IR <utime.h> .
.IP
Used for time in seconds.
According to POSIX, it shall be an integer type.
.IP
Conforming to: C99 and later; POSIX.1-2001 and later.
.IP
Notes:
.I <sched.h>
defines
.I time_t
since POSIX.1-2008.
.IP
See also:
.BR stime (2),
.BR time (2),
.BR ctime (3),
.BR difftime (3)
.\"------------------------------------- timer_t ----------------------/
.TP
.I timer_t
.IP
Include:
.IR <sys/types.h> ;
or
.IR <time.h> .
.IP
Used for timer ID returned by
.BR timer_create (2).
According to POSIX,
there are no defined comparison or assignment operators for this type.
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR timer_create (2),
.BR timer_delete (2),
.BR timer_getoverrun (2),
.BR timer_settime (2)
.\"------------------------------------- timespec ---------------------/
.TP
.I timespec
.IP
Include:
.IR <time.h> ;
or
.I <aio.h>
or
.I <mqueue.h>
or
.I <sched.h>
or
.I <signal.h>
or
.I <sys/select.h>
or
.IR <sys/stat.h> .
.IP
.EX
struct timespec {
    time_t  tv_sec;  /* Seconds */
    long    tv_nsec; /* Nanoseconds */
};
.EE
.IP
Describes times in seconds and nanoseconds.
.IP
Conforming to: C11 and later; POSIX.1-2001 and later.
.IP
See also:
.BR clock_gettime (2),
.BR clock_nanosleep (2),
.BR nanosleep (2),
.BR timerfd_gettime (2),
.BR timer_gettime (2)
.\"------------------------------------- timeval ----------------------/
.TP
.I timeval
.IP
Include:
.IR <sys/time.h> ;
or
.I <sys/resource.h>
or
.I <sys/select.h>
or
.IR <utmpx.h> .
.IP
.EX
struct timeval {
    time_t      tv_sec;  /* Seconds */
    suseconds_t tv_usec; /* Microseconds */
};
.EE
.IP
Describes times in seconds and microseconds.
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR gettimeofday (2),
.BR select (2),
.BR utimes (2),
.BR adjtime (3),
.BR futimes (3),
.BR timeradd (3)
.\"------------------------------------- uid_t ----------------------/
.TP
.I uid_t
.IP
Include:
.IR <sys/types.h> ;
or
.I <pwd.h>
or
.I <signal.h>
or
.I <stropts.h>
or
.I <sys/ipc.h>
or
.I <sys/stat.h>
or
.IR <unistd.h> .
.IP
A type used to hold user IDs.
According to POSIX,
this shall be an integer type.
.IP
Conforming to: POSIX.1-2001 and later.
.IP
See also:
.BR chown (2),
.BR getuid (2),
.BR geteuid (2),
.BR getresuid (2),
.BR getpwnam (2),
.BR credentials (7)
.SH NOTES
The structures described in this manual page shall contain,
at least, the members shown in their definition, in no particular order.
.PP
Most of the integer types described in this page don't have
a corresponding length modifier for the
.BR printf (3)
and the
.BR 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
.I intmax_t
or
.I 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
.I intmax_t
or
.I 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.
.SH 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
.IR intmax_t ,
and the appropriate range checks,
are used as explained in the notes section above.
.PP
.EX
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>

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!\en");
        exit(EXIT_FAILURE);
    }

    /* Copy the value to the suseconds_t variable \(aqus\(aq */

    us = tmp;

    /* Even though suseconds_t can hold the value \-1, this isn\(aqt
       a sensible number of microseconds */

    if (us < 0) {
        fprintf(stderr, "Scanned value shouldn\(aqt be negative!\en");
        exit(EXIT_FAILURE);
    }

    /* Print the value */

    printf("There are %jd microseconds in half a second.\en",
            (intmax_t) us);

    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR feature_test_macros (7),
.BR standards (7)