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SYSTEM_DATA_TYPES(7)                Linux Programmer's Manual                SYSTEM_DATA_TYPES(7)

NAME
       system_data_types - overview of system data types

DESCRIPTION
       aiocb
              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)

       clock_t
              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>).   Ac-
              cording 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: <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)

       dev_t
              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)

       div_t
              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)

       double_t
              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-de-
              fined.

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

              See also: the float_t type in this page.

       fd_set
              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)

       fenv_t
              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)

       fexcept_t
              Include: <fenv.h>.

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

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

              See also: fenv(3)

       FILE
              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)

       float_t
              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.

       gid_t
              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)

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

              A type used to hold a general identifier.  According to POSIX, this shall be an in-
              teger 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: <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)

       intmax_t
              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  imple-
              mentations 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: <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 speci-
              fied 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 appro-
              priate number.

              According to POSIX, int8_t, int16_t, and int32_t are required; int64_t is only  re-
              quired  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>); result-
              ing 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 exam-
              ple 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: <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  stor-
              ing 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.

       lconv
              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)

       ldiv_t
              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)

       lldiv_t
              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)

       off_t
              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)

       pid_t
              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.  Ac-
              cording  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),  creden-
              tials(7),

       ptrdiff_t
              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.

       regex_t
              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)

       regmatch_t
              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)

       regoff_t
              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.

       sigevent
              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.

       siginfo_t
              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  (in-
              cluding 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: <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), sigpend-
              ing(2), sigprocmask(2), sigsuspend(2), sigwaitinfo(2), signal(7)

       sigval
              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.

       size_t
              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 func-
              tions 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.

       ssize_t
              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  environ-
              ments 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 im-
              plementations, portable POSIX programs should avoid using it--for example, by  con-
              verting 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: <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  imple-
              mentation  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:  <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)

       timer_t
              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)

       timespec
              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)

       timeval
              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), timer-
              add(3)

       uid_t
              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), creden-
              tials(7)

       uintmax_t
              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  uint-
              max_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: <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 appro-
              priate 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)  fam-
              ily 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.

       uintptr_t
              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>); re-
              sulting  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>); re-
              sulting 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: <stdarg>.  Alternatively, <stdio.h>, or <wchar.h>.

              Used by functions with a varying number of arguments of varying types.   The  func-
              tion  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  argu-
              ments.

              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  pro-
              grammer  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  modi-
       fier for the printf(3) and the scanf(3) families of functions.  To print a value of an in-
       teger 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  ei-
       ther  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 <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!\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/.

Linux                                       2020-12-21                       SYSTEM_DATA_TYPES(7)

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