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Diffstat (limited to 'lib/libc/stdtime/time2posix.3')
| -rw-r--r-- | lib/libc/stdtime/time2posix.3 | 114 |
1 files changed, 0 insertions, 114 deletions
diff --git a/lib/libc/stdtime/time2posix.3 b/lib/libc/stdtime/time2posix.3 deleted file mode 100644 index 38bb1ab..0000000 --- a/lib/libc/stdtime/time2posix.3 +++ /dev/null @@ -1,114 +0,0 @@ -.Dd May 1, 1996 -.Dt TIME2POSIX 3 -.Os -.Sh NAME -.Nm time2posix , -.Nm posix2time -.Nd convert seconds since the Epoch -.Sh SYNOPSIS -.Fd #include <time.h> -.Ft time_t -.Fn time2posix "const time_t *t" -.Ft time_t -.Fn posix2time "const time_t *t" -.Sh DESCRIPTION -.St -p1003.1-88 -legislates that a time_t value of -536457599 shall correspond to "Wed Dec 31 23:59:59 GMT 1986." -This effectively implies that POSIX time_t's cannot include leap -seconds and, -therefore, -that the system time must be adjusted as each leap occurs. -.Pp -If the time package is configured with leap-second support -enabled, -however, -no such adjustment is needed and -time_t values continue to increase over leap events -(as a true `seconds since...' value). -This means that these values will differ from those required by POSIX -by the net number of leap seconds inserted since the Epoch. -.Pp -Typically this is not a problem as the type time_t is intended -to be -(mostly) -opaque\(emtime_t values should only be obtained-from and -passed-to functions such as -.Xr time 2 , -.Xr localtime 3 , -.Xr mktime 3 -and -.Xr difftime 3 . -However, -.Std -p1003.1-88 -gives an arithmetic -expression for directly computing a time_t value from a given date/time, -and the same relationship is assumed by some -(usually older) -applications. -Any programs creating/dissecting time_t's -using such a relationship will typically not handle intervals -over leap seconds correctly. -.Pp -The -.Fn time2posix -and -.Fn posix2time -functions are provided to address this time_t mismatch by converting -between local time_t values and their POSIX equivalents. -This is done by accounting for the number of time-base changes that -would have taken place on a POSIX system as leap seconds were inserted -or deleted. -These converted values can then be used in lieu of correcting the older -applications, -or when communicating with POSIX-compliant systems. -.Pp -The -.Fn time2posix -function is single-valued. -That is, -every local time_t -corresponds to a single POSIX time_t. -The -.Fn posix2time -function is less well-behaved: -for a positive leap second hit the result is not unique, -and for a negative leap second hit the corresponding -POSIX time_t doesn't exist so an adjacent value is returned. -Both of these are good indicators of the inferiority of the -POSIX representation. -.Pp -The following table summarizes the relationship between time_t -and its conversion to, -and back from, -the POSIX representation over the leap second inserted at the end of June, -1993. -.ta \w'93/06/30 'u +\w'23:59:59 'u +\w'A+0 'u +\w'X=time2posix(T) 'u -DATE TIME T X=time2posix(T) posix2time(X) -93/06/30 23:59:59 A+0 B+0 A+0 -93/06/30 23:59:60 A+1 B+1 A+1 or A+2 -93/07/01 00:00:00 A+2 B+1 A+1 or A+2 -93/07/01 00:00:01 A+3 B+2 A+3 - -A leap second deletion would look like... - -DATE TIME T X=time2posix(T) posix2time(X) -??/06/30 23:59:58 A+0 B+0 A+0 -??/07/01 00:00:00 A+1 B+2 A+1 -??/07/01 00:00:01 A+2 B+3 A+2 -.Pp - [Note: posix2time(B+1) => A+0 or A+1] -.Pp -If leap-second support is not enabled, -local time_t's and -POSIX time_t's are equivalent, -and both -.Fn time2posix -and -.Fn posix2time -degenerate to the identity function. -.Sh "SEE ALSO" -.Xr difftime 3 , -.Xr localtime 3 , -.Xr mktime 3 , -.Xr time 3 |
