diff options
Diffstat (limited to 'time/time2posix.3')
| -rw-r--r-- | time/time2posix.3 | 119 |
1 files changed, 0 insertions, 119 deletions
diff --git a/time/time2posix.3 b/time/time2posix.3 deleted file mode 100644 index 846a52ed1..000000000 --- a/time/time2posix.3 +++ /dev/null @@ -1,119 +0,0 @@ -.TH TIME2POSIX 3 -.SH NAME -time2posix, posix2time \- convert seconds since the Epoch -.SH SYNOPSIS -.nf -.B #include <sys/types.h> -.B #include <time.h> -.PP -.B time_t time2posix(t) -.B time_t t -.PP -.B time_t posix2time(t) -.B time_t t -.PP -.B cc ... -lz -.fi -.SH DESCRIPTION -IEEE Standard 1003.1 -(POSIX) -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 -.IR time(2) , -.IR localtime(3) , -.IR mktime(3) , -and -.IR difftime(3) . -However, -POSIX 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 -.I time2posix -and -.I 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 -.I Time2posix -is single-valued. -That is, -every local time_t -corresponds to a single POSIX time_t. -.I Posix2time -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 a time -T and it's conversion to, -and back from, -the POSIX representation over the leap second inserted at the end of June, -1993. -.nf -.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 -.sp -.ce - [Note: posix2time(B+1) => A+0 or A+1] -.fi -.PP -If leap-second support is not enabled, -local time_t's and -POSIX time_t's are equivalent, -and both -.I time2posix -and -.I posix2time -degenerate to the identity function. -.SH SEE ALSO -difftime(3), -localtime(3), -mktime(3), -time(2) -.\" @(#)time2posix.3 7.3 |