преобразовать дату и время в строку (convert date and time to a string)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
asctime, asctime_r — convert date and time to a string
Синопсис (Synopsis)
#include <time.h>
char *asctime(const struct tm *timeptr);
char *asctime_r(const struct tm *restrict tm, char *restrict buf);
Описание (Description)
For asctime(): The functionality described on this reference page
is aligned with the ISO C standard. Any conflict between the
requirements described here and the ISO C standard is
unintentional. This volume of POSIX.1‐2017 defers to the ISO C
standard.
The asctime() function shall convert the broken-down time in the
structure pointed to by timeptr into a string in the form:
Sun Sep 16 01:03:52 1973\n\0
using the equivalent of the following algorithm:
char *asctime(const struct tm *timeptr)
{
static char wday_name[7][3] = {
"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
};
static char mon_name[12][3] = {
"Jan", "Feb", "Mar", "Apr", "May", "Jun",
"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};
static char result[26];
sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
wday_name[timeptr->tm_wday],
mon_name[timeptr->tm_mon],
timeptr->tm_mday, timeptr->tm_hour,
timeptr->tm_min, timeptr->tm_sec,
1900 + timeptr->tm_year);
return result;
}
However, the behavior is undefined if timeptr->tm_wday or
timeptr->tm_mon are not within the normal ranges as defined in
<time.h>, or if timeptr->tm_year exceeds {INT_MAX}-1990, or if
the above algorithm would attempt to generate more than 26 bytes
of output (including the terminating null).
The tm structure is defined in the <time.h> header.
The asctime(), ctime(), gmtime(), and localtime() functions shall
return values in one of two static objects: a broken-down time
structure and an array of type char. Execution of any of the
functions may overwrite the information returned in either of
these objects by any of the other functions.
The asctime() function need not be thread-safe.
The asctime_r() function shall convert the broken-down time in
the structure pointed to by tm into a string (of the same form as
that returned by asctime(), and with the same undefined behavior
when input or output is out of range) that is placed in the user-
supplied buffer pointed to by buf (which shall contain at least
26 bytes) and then return buf.
Возвращаемое значение (Return value)
Upon successful completion, asctime() shall return a pointer to
the string. If the function is unsuccessful, it shall return
NULL.
Upon successful completion, asctime_r() shall return a pointer to
a character string containing the date and time. This string is
pointed to by the argument buf. If the function is unsuccessful,
it shall return NULL.
Ошибки (Error)
No errors are defined.
The following sections are informative.
Примеры (Examples)
None.
Использование в приложениях (Application usage)
These functions are included only for compatibility with older
implementations. They have undefined behavior if the resulting
string would be too long, so the use of these functions should be
discouraged. On implementations that do not detect output string
length overflow, it is possible to overflow the output buffers in
such a way as to cause applications to fail, or possible system
security violations. Also, these functions do not support
localized date and time formats. To avoid these problems,
applications should use strftime() to generate strings from
broken-down times.
Values for the broken-down time structure can be obtained by
calling gmtime() or localtime().
The asctime_r() function is thread-safe and shall return values
in a user-supplied buffer instead of possibly using a static data
area that may be overwritten by each call.
Обоснование (Rationale)
The standard developers decided to mark the asctime() and
asctime_r() functions obsolescent even though asctime() is in the
ISO C standard due to the possibility of buffer overflow. The
ISO C standard also provides the strftime() function which can be
used to avoid these problems.
Будущие направления (Future directions)
These functions may be removed in a future version.
Смотри также (See also)
clock(3p), ctime(3p), difftime(3p), gmtime(3p), localtime(3p),
mktime(3p), strftime(3p), strptime(3p), time(3p), utime(3p)
The Base Definitions volume of POSIX.1‐2017, time.h(0p)
