SEE ALSO

login(1), passwd(1), encrypt(3), getpass(3), passwd(5)

3 September 1994

ctermid

ctermid—Gets controlling terminal name

SYNOPSIS

#include <stdio.h>
char *ctermid(char *s);

DESCRIPTION

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.

RETURN VALUE

This function returns the pointer to the pathname.

CONFORMS TO

POSIX.1

BUGS

The path returned might not uniquely identify the controlling terminal; it might, for example, be /dev/tty.

It is not assured that the program can open the terminal.

SEE ALSO

ttyname(3)

GNU, 6 April 1993

asctime, ctime, gmtime, localtime, mktime

asctime, ctime, gmtime, localtime, mktime

—Transform binary date and time to ASCII

SYNOPSIS

#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;

DESCRIPTION

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).

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:

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 */
};

The members of the tm structure are

tm_sec	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.
tm_min	The number of minutes after the hour, in the range 0 to 59.
tm_hour	The number of hours past midnight, in the range 0 to 23.
tm_mday	The day of the month, in the range 1 to 31.
tm_mon	The number of months since January, in the range 0 to 11.
tm_year	The number of years since 1900.
tm_wday	The number of days since Sunday, in the range 0 to 6.
tm_yday	The number of days since January 1, in the range 0 to 365.
tm_isdst	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.

The ctime()function converts the calendar time timep into a string of the form

"Wed Jun 30 21:49:08 1993\n"

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.

The gmtime() function converts the calendar time timep to broken-down time representation, expressed in Coordinated Universal Time (UTC).

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.

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.

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.