Originální popis anglicky:
localtime, localtime_r - convert a time value to a broken-down local time
Návod, kniha: POSIX Programmer's Manual
#include <time.h>
struct tm *localtime(const time_t *
timer);
struct tm *localtime_r(const time_t *restrict timer,
struct tm *restrict
result );
For
localtime(): 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
IEEE Std 1003.1-2001 defers to the ISO C standard.
The
localtime() function shall convert the time in seconds since the
Epoch pointed to by
timer into a broken-down time, expressed as a local
time. The function corrects for the timezone and any seasonal time
adjustments. Local timezone information is used as though
localtime() calls
tzset().
The relationship between a time in seconds since the Epoch used as an argument
to
localtime() and the
tm structure (defined in the
<time.h> header) is that the result shall be as specified in the
expression given in the definition of seconds since the Epoch (see the Base
Definitions volume of IEEE Std 1003.1-2001, Section 4.14,
Seconds Since the Epoch) corrected for timezone and any seasonal time
adjustments, where the names in the structure and in the expression
correspond.
The same relationship shall apply for
localtime_r().
The
localtime() function need not be reentrant. A function that is not
required to be reentrant is not required to be thread-safe.
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
localtime_r() function shall convert the time in seconds since the
Epoch pointed to by
timer into a broken-down time stored in the
structure to which
result points. The
localtime_r() function
shall also return a pointer to that same structure.
Unlike
localtime(), the reentrant version is not required to set
tzname.
Upon successful completion, the
localtime() function shall return a
pointer to the broken-down time structure. If an error is detected,
localtime() shall return a null pointer and set
errno to
indicate the error.
Upon successful completion,
localtime_r() shall return a pointer to the
structure pointed to by the argument
result.
The
localtime() function shall fail if:
- EOVERFLOW
- The result cannot be represented.
The following sections are informative.
The following example uses the
time() function to calculate the time
elapsed, in seconds, since January 1, 1970 0:00 UTC (the Epoch),
localtime() to convert that value to a broken-down time, and
asctime() to convert the broken-down time values into a printable
string.
#include <stdio.h>
#include <time.h>
int main(void)
{
time_t result;
result = time(NULL);
printf("%s%ju secs since the Epoch\n",
asctime(localtime(&result)),
(uintmax_t)result);
return(0);
}
This example writes the current time to
stdout in a form like this:
Wed Jun 26 10:32:15 1996
835810335 secs since the Epoch
The following example gets the modification time for a file. The
localtime() function converts the
time_t value of the last
modification date, obtained by a previous call to
stat(), into a
tm structure that contains the year, month, day, and so on.
#include <time.h>
...
struct stat statbuf;
...
tm = localtime(&statbuf.st_mtime);
...
The following example gets the current time, converts it to a string using
localtime() and
asctime(), and prints it to standard output
using
fputs(). It then prints the number of minutes to an event being
timed.
#include <time.h>
#include <stdio.h>
...
time_t now;
int minutes_to_event;
...
time(&now);
printf("The time is ");
fputs(asctime(localtime(&now)), stdout);
printf("There are still %d minutes to the event.\n",
minutes_to_event);
...
The
localtime_r() function is thread-safe and returns values in a
user-supplied buffer instead of possibly using a static data area that may be
overwritten by each call.
None.
None.
asctime() ,
clock() ,
ctime() ,
difftime() ,
getdate() ,
gmtime() ,
mktime() ,
strftime() ,
strptime() ,
time() ,
utime() , the Base Definitions
volume of IEEE Std 1003.1-2001,
<time.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
