localtime.3p (6968B)
- '\" et
- .TH LOCALTIME "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH 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.
- .\"
- .SH NAME
- localtime,
- localtime_r
- \(em convert a time value to a broken-down local time
- .SH SYNOPSIS
- .LP
- .nf
- #include <time.h>
- .P
- struct tm *localtime(const time_t *\fItimer\fP);
- struct tm *localtime_r(const time_t *restrict \fItimer\fP,
- struct tm *restrict \fIresult\fP);
- .fi
- .SH DESCRIPTION
- For
- \fIlocaltime\fR():
- 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\(hy2017 defers to the ISO\ C standard.
- .P
- The
- \fIlocaltime\fR()
- function shall convert the time in seconds since the Epoch pointed
- to by
- .IR 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
- \fIlocaltime\fR()
- calls
- \fItzset\fR().
- .P
- The relationship between a time in seconds since the Epoch used as an
- argument to
- \fIlocaltime\fR()
- and the
- .BR tm
- structure (defined in the
- .IR <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 POSIX.1\(hy2017,
- .IR "Section 4.16" ", " "Seconds Since the Epoch")
- corrected for timezone and any seasonal time adjustments, where the
- names in the structure and in the expression correspond.
- .P
- The same relationship shall apply for
- \fIlocaltime_r\fR().
- .P
- The
- \fIlocaltime\fR()
- function need not be thread-safe.
- .P
- The
- \fIasctime\fR(),
- \fIctime\fR(),
- \fIgmtime\fR(),
- and
- \fIlocaltime\fR()
- functions shall return values in one of two static objects: a
- broken-down time structure and an array of type
- .BR char .
- Execution of any of the functions may overwrite the information
- returned in either of these objects by any of the other functions.
- .P
- The
- \fIlocaltime_r\fR()
- function shall convert the time in seconds since the Epoch pointed
- to by
- .IR timer
- into a broken-down time stored in the structure to which
- .IR result
- points. The
- \fIlocaltime_r\fR()
- function shall also return a pointer to that same structure.
- .P
- Unlike
- \fIlocaltime\fR(),
- the
- \fIlocaltime_r\fR()
- function is not required to set
- .IR tzname .
- If
- \fIlocaltime_r\fR()
- sets
- .IR tzname ,
- it shall also set
- .IR daylight
- and
- .IR timezone .
- If
- \fIlocaltime_r\fR()
- does not set
- .IR tzname ,
- it shall not set
- .IR daylight
- and shall not set
- .IR timezone .
- .SH "RETURN VALUE"
- Upon successful completion, the
- \fIlocaltime\fR()
- function shall return a pointer to the broken-down time structure.
- If an error is detected,
- \fIlocaltime\fR()
- shall return a null pointer
- and set
- .IR errno
- to indicate the error.
- .P
- Upon successful completion,
- \fIlocaltime_r\fR()
- shall return a pointer to the structure pointed to by the argument
- .IR result .
- If an error is detected,
- \fIlocaltime_r\fR()
- shall return a null pointer and set
- .IR errno
- to indicate the error.
- .SH ERRORS
- The
- \fIlocaltime\fR()
- and
- \fIlocaltime_r\fR()
- functions shall fail if:
- .TP
- .BR EOVERFLOW
- The result cannot be represented.
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- .SS "Getting the Local Date and Time"
- .P
- The following example uses the
- \fItime\fR()
- function to calculate the time elapsed, in seconds, since January 1,
- 1970 0:00 UTC (the Epoch),
- \fIlocaltime\fR()
- to convert that value to a broken-down time, and
- \fIasctime\fR()
- to convert the broken-down time values into a printable string.
- .sp
- .RS 4
- .nf
- #include <stdio.h>
- #include <time.h>
- .P
- int main(void)
- {
- time_t result;
- .P
- result = time(NULL);
- printf("%s%ju secs since the Epoch\en",
- asctime(localtime(&result)),
- (uintmax_t)result);
- return(0);
- }
- .fi
- .P
- .RE
- .P
- This example writes the current time to
- .IR stdout
- in a form like this:
- .sp
- .RS 4
- .nf
- Wed Jun 26 10:32:15 1996
- 835810335 secs since the Epoch
- .fi
- .P
- .RE
- .SS "Getting the Modification Time for a File"
- .P
- The following example prints the last data modification timestamp
- in the local timezone for a given file.
- .sp
- .RS 4
- .nf
- #include <stdio.h>
- #include <time.h>
- #include <sys/stat.h>
- .P
- int
- print_file_time(const char *pathname)
- {
- struct stat statbuf;
- struct tm *tm;
- char timestr[BUFSIZ];
- .P
- if(stat(pathname, &statbuf) =\|= -1)
- return -1;
- if((tm = localtime(&statbuf.st_mtime)) =\|= NULL)
- return -1;
- if(strftime(timestr, sizeof(timestr), "%Y-%m-%d %H:%M:%S", tm) =\|= 0)
- return -1;
- printf("%s: %s.%09ld\en", pathname, timestr, statbuf.st_mtim.tv_nsec);
- return 0;
- }
- .fi
- .P
- .RE
- .SS "Timing an Event"
- .P
- The following example gets the current time, converts it to a string
- using
- \fIlocaltime\fR()
- and
- \fIasctime\fR(),
- and prints it to standard output using
- \fIfputs\fR().
- It then prints the number of minutes to an event being timed.
- .sp
- .RS 4
- .nf
- #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.\en",
- minutes_to_event);
- \&...
- .fi
- .P
- .RE
- .SH "APPLICATION USAGE"
- The
- \fIlocaltime_r\fR()
- 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.
- .SH RATIONALE
- None.
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "\fIasctime\fR\^(\|)",
- .IR "\fIclock\fR\^(\|)",
- .IR "\fIctime\fR\^(\|)",
- .IR "\fIdifftime\fR\^(\|)",
- .IR "\fIgetdate\fR\^(\|)",
- .IR "\fIgmtime\fR\^(\|)",
- .IR "\fImktime\fR\^(\|)",
- .IR "\fIstrftime\fR\^(\|)",
- .IR "\fIstrptime\fR\^(\|)",
- .IR "\fItime\fR\^(\|)",
- .IR "\fItzset\fR\^(\|)",
- .IR "\fIutime\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "Section 4.16" ", " "Seconds Since the Epoch",
- .IR "\fB<time.h>\fP"
- .\"
- .SH COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
- from IEEE Std 1003.1-2017, Standard for Information Technology
- -- Portable Operating System Interface (POSIX), The Open Group Base
- Specifications Issue 7, 2018 Edition,
- Copyright (C) 2018 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 .
- .PP
- Any typographical or formatting errors that appear
- in this page are most likely
- to have been introduced during the conversion of the source files to
- man page format. To report such errors, see
- https://www.kernel.org/doc/man-pages/reporting_bugs.html .