system_data_types - overview of system data types
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>
). According to POSIX, it shall be an integer type or a real-floating type.
Conforming to
: C99 and later; POSIX.1-2001 and later.
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.
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
isdouble
.- 1
double_t
isdouble
.- 2
double_t
islong 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
: thefloat_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 details 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
isfloat
.- 1
float_t
isdouble
.- 2
float_t
islong 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
: thedouble_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 integer type that can be used to contain a
pid_t
,uid_t
, orgid_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 printingintmax_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 andlong long
is less than 128 bits wide.
See also
: theuintmax_t
type in this page.
int
N_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 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
, andint32_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
int
N_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 printingint64_t
values. The length modifiers for theint
N_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 scanningint8_t
values.
Conforming to
: C99 and later; POSIX.1-2001 and later.
See also
: theintmax_t
,uint
N_t
, anduintmax_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 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 printingintptr_t
values. The length modifier forintptr_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 scanningintptr_t
values.
Conforming to
: C99 and later; POSIX.1-2001 and later.
See also
: theuintptr_t
andvoid *
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>
defineoff_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. 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 typelong
.
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
:<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 printingptrdiff_t
values.
Conforming to
: C99 and later; POSIX.1-2001 and later.
See also
: thesize_t
andssize_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 assize_t
type.
Versions
: Prior to POSIX.1-2008, the type was capable of storing the largest value that can be stored in either anoff_t
type or assize_t
type.
Conforming to
: POSIX.1-2001 and later.
See also
: theregmatch_t
structure and theptrdiff_t
andssize_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>
definesigevent
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 (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
:<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)
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 thesiginfo_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 ofsize_t
is no greater than the width of the typelong
.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 printingsize_t
values.
Versions
:<aio.h>
,<glob.h>
,<grp.h>
,<iconv.h>
,<mqueue.h>
,<pwd.h>
,<signal.h>
, and<sys/socket.h>
definesize_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
andssize_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 environments where the width of
ssize_t
is no greater than the width of the typelong
.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 printingssize_t
values. Although z works forssize_t
on most implementations, portable POSIX programs should avoid using it—for example, by converting the value tointmax_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
andsize_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 implementation shall support one or more programming environments where the width of
suseconds_t
is no greater than the width of the typelong
.
Conforming to
: POSIX.1-2001 and later.
See also
: thetimeval
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>
definestime_t
since POSIX.1-2008.
Conforming to
: C99 and later; POSIX.1-2001 and later.
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), timeradd(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), credentials(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
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 printinguintmax_t
values.
Conforming to
: C99 and later; POSIX.1-2001 and later.
Bugs
:uintmax_t
is not large enough to represent values of typeunsigned __int128
in implementations whereunsigned __int128
is defined andunsigned long long
is less than 128 bits wide.
See also
: theintmax_t
type in this page.
uint
N_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 appropriate number.
According to POSIX,
uint8_t
,uint16_t
, anduint32_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
uint
N_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 printinguint32_t
values. The length modifiers for theuint
N_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 scanninguint16_t
values.
Conforming to
: C99 and later; POSIX.1-2001 and later.
See also
: theintmax_t
,int
N_t
, anduintmax_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>
); resulting commonly in %"PRIuPTR" or %"PRIxPTR" for printinguintptr_t
values. The length modifier foruintptr_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 scanninguintptr_t
values.
Conforming to
: C99 and later; POSIX.1-2001 and later.
See also
: theintptr_t
andvoid *
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 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.
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 tovoid
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 avoid
or of a function as 1. A consequence of this is thatsizeof
is also allowed onvoid
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 betweenvoid *
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
anduintptr_t
types in this page.
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.
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.
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);
}
feature_test_macros(7), standards(7)
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https://www.kernel.org/doc/man-pages/.