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<TITLE>Linux Complete Command Reference:Library Functions:EarthWeb Inc.-</TITLE>
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<!-- ISBN=0672311046 //-->
<!-- TITLE=Linux Complete Command Reference//-->
<!-- AUTHOR=Red Hat//-->
<!-- PUBLISHER=Macmillan Computer Publishing//-->
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<!-- CHAPTER=03 //-->
<!-- PAGES=0891-1062 //-->
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<a href="0905-0908.html">Previous</A> | <a href="../ewtoc.html">Table of Contents</A> | <a href="0911-0913.html">Next</A></CENTER></P>
<A NAME="PAGENUM-909"><P>Page 909</P></A>
<P></B>SEE ALSO</B>
</P>
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<PRE>
login(1), passwd(1), encrypt(3), getpass(3), passwd(5)
</PRE>
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<P>3 September 1994
</P>
<H3><A NAME="ch03_ 35">
ctermid
</A></H3>
<P>ctermid—Gets controlling terminal name
</P>
<P><B>SYNOPSIS</B>
</P>
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<PRE WIDTH="1">
#include <stdio.h>
char *ctermid(char *s);
</PRE>
<!-- END CODE SNIP //-->
<P><B>DESCRIPTION</B>
</P>
<P>ctermid() returns a string that is the pathname for the current controlling terminal for this process. If
s is NULL, a static buffer is used; otherwise, s points to a buffer used to hold the terminal pathname. The symbolic constant
L_ctermid is the maximum number of characters in the returned pathname.
</P>
<P><B>RETURN VALUE</B>
</P>
<P>This function returns the pointer to the pathname.
</P>
<P><B>CONFORMS TO</B>
</P>
<P>POSIX.1
</P>
<P><B>BUGS</B>
</P>
<P>The path returned might not uniquely identify the controlling terminal; it might, for example, be
/dev/tty.
</P>
<P>It is not assured that the program can open the terminal.
</P>
<P></B>SEE ALSO</B>
</P>
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<PRE>
ttyname(3)
</PRE>
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<P>GNU, 6 April 1993
</P>
<H3><A NAME="ch03_ 36">
asctime, ctime, gmtime, localtime, mktime
</A></H3>
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<PRE>
asctime, ctime, gmtime, localtime, mktime
</PRE>
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<P>—Transform binary date and time to ASCII
</P>
<P><B>SYNOPSIS</B>
</P>
<!-- CODE //-->
<PRE WIDTH="1">
#include <time.h>
char *asctime(const struct tm *timeptr);
char *ctime(const time_t *timep);
struct tm *gmtime(const time_t *timep);
struct tm *localtime(const time_t *timep);
time_t mktime(struct tm *timeptr);
extern char *tzname[2];
long int timezone;
extern int daylight;
</PRE>
<!-- END CODE //-->
<P><B>DESCRIPTION</B>
</P>
<P>The ctime(), gmtime(), and localtime()functions all take an argument of data type
time_t, which represents calendar time. When interpreted as an absolute time value, it represents the number of seconds elapsed since 00:00:00 on January 1,
1970, Coordinated Universal Time (UTC).
</P>
<A NAME="PAGENUM-910"><P>Page 910</P></A>
<P>The asctime() and mktime() functions both take an argument representing broken-down time, which is a binary
representation separated into year, month, day, and so on. Broken-down time is stored in the structure
tm, which is defined in <time.h> as follows:
</P>
<!-- CODE //-->
<PRE WIDTH="1">
struct tm
{
int tm_sec; /* seconds */
int tm_min; /* minutes */
int tm_hour; /* hours */
int tm_mday; /* day of the month */
int tm_mon; /* month */
int tm_year; /* year */
int tm_wday; /* day of the week */
int tm_yday; /* day in the year */
int tm_isdst; /* daylight saving time */
};
</PRE>
<!-- END CODE //-->
<P>The members of the tm structure are
<TABLE>
<TR><TD>
tm_sec
</TD><TD>
The number of seconds after the minute, normally in the range 0 to 59, but can be up to 61 to allow
for leap seconds.
</TD></TR><TR><TD>
tm_min
</TD><TD>
The number of minutes after the hour, in the range 0 to 59.
</TD></TR><TR><TD>
tm_hour
</TD><TD>
The number of hours past midnight, in the range 0 to 23.
</TD></TR><TR><TD>
tm_mday
</TD><TD>
The day of the month, in the range 1 to 31.
</TD></TR><TR><TD>
tm_mon
</TD><TD>
The number of months since January, in the range 0 to 11.
</TD></TR><TR><TD>
tm_year
</TD><TD>
The number of years since 1900.
</TD></TR><TR><TD>
tm_wday
</TD><TD>
The number of days since Sunday, in the range 0 to 6.
</TD></TR><TR><TD>
tm_yday
</TD><TD>
The number of days since January 1, in the range 0 to 365.
</TD></TR><TR><TD>
tm_isdst
</TD><TD>
A flag that indicates whether daylight savings time is in effect at the time described. The value is positive
if daylight saving time is in effect, 0 if it is not, and negative if the information is not available.
</TD></TR></TABLE>
<P>The ctime()function converts the calendar time
timep into a string of the form
<!-- CODE SNIP //-->
<PRE>
"Wed Jun 30 21:49:08 1993\n"
</PRE>
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<P>The abbreviations for the days of the week are
Sun, Mon , Tue, Wed, Thu, Fri, and Sat. The abbreviations for the months
are Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep,
Oct, Nov, and Dec. The return value points to a statically allocated string that
might be overwritten by subsequent calls to any of the date and time functions. The function also sets the external variable
tzname with information about the current time zone.
<P>The gmtime() function converts the calendar time timep to broken-down time representation, expressed in
Coordinated Universal Time (UTC).
<P>The localtime() function converts the calendar time
timep to broken-time representation, expressed relative to the
user's specified time zone. The function sets the external variables
tzname with information about the current time zone,
timezone with the difference between Coordinated Universal Time and local standard time in seconds, and
daylight to a nonzero value if standard U.S. daylight saving time rules apply.
<P>The asctime() function converts the broken-down time value
timeptr into a string with the same format as
ctime(). The return value points to a statically allocated string that might be overwritten by subsequent calls to any of the date and
time functions.
<P>The mktime() function converts a broken-down time structure, expressed as local time, to calendar time representation.
The function ignores the specified contents of the structure members
tm_wday and tm_yday and recomputes them from the
other information in the broken-down time structure. Calling
mktime() also sets the external variable tzname with
information about the current time zone. If the specified broken-down time cannot be represented as calendar time,
mktime() returns a value of (time_t)(_1) and does not alter the
tm_wday and tm_yday members of the broken-down time structure.
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