.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "GMTIME" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" gmtime 
.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
gmtime, gmtime_r \- convert a time value to a broken-down UTC time
.SH SYNOPSIS
.LP
\fB#include <time.h>
.br
.sp
struct tm *gmtime(const time_t *\fP\fItimer\fP\fB);
.br
\fP
.LP
\fBstruct tm *gmtime_r(const time_t *restrict\fP \fItimer\fP\fB,
.br
\ \ \ \ \ \  struct tm *restrict\fP \fIresult\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
For \fIgmtime\fP():   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. 
.LP
The \fIgmtime\fP() function shall convert the time in seconds since
the Epoch pointed to by \fItimer\fP into a broken-down
time, expressed as Coordinated Universal Time (UTC).
.LP
The
relationship between a time in seconds since the Epoch used as an
argument to \fIgmtime\fP() and the \fBtm\fP structure (defined
in the \fI<time.h>\fP 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), where the names in the structure
and in
the expression correspond. 
.LP
The same relationship shall apply for \fIgmtime_r\fP(). 
.LP
The
\fIgmtime\fP() function need not be reentrant. A function that is
not required to be reentrant is not required to be
thread-safe.
.LP
The \fIasctime\fP(), \fIctime\fP(),
\fIgmtime\fP(), and \fIlocaltime\fP() functions shall return values
in one of two
static objects: a broken-down time structure and an array of type
\fBchar\fP. Execution of any of the functions may overwrite the
information returned in either of these objects by any of the other
functions. 
.LP
The \fIgmtime_r\fP() function shall convert the time in seconds since
the Epoch pointed to by \fItimer\fP into a broken-down time
expressed as Coordinated Universal Time (UTC). The broken-down time
is stored in the structure referred to by \fIresult\fP. The
\fIgmtime_r\fP() function shall also return the address of the same
structure. 
.SH RETURN VALUE
.LP
Upon successful completion, the \fIgmtime\fP() function shall return
a pointer to a \fBstruct tm\fP. If an error is detected,
\fIgmtime\fP() shall return a null pointer  and set \fIerrno\fP
to indicate the error. 
.LP
Upon successful completion, \fIgmtime_r\fP() shall return the address
of the structure pointed to by the argument \fIresult\fP.
If an error is detected, \fIgmtime_r\fP() shall return a null pointer.
.SH ERRORS
.LP
The \fIgmtime\fP() function shall fail if:
.TP 7
.B EOVERFLOW
The result cannot be represented. 
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
The \fIgmtime_r\fP() 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
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIasctime\fP(), \fIclock\fP(), \fIctime\fP(),
\fIdifftime\fP(), \fIlocaltime\fP(), \fImktime\fP(), \fIstrftime\fP(),
\fIstrptime\fP(),
\fItime\fP(), \fIutime\fP(), the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, \fI<time.h>\fP
.SH COPYRIGHT
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 .