The Unix standard defines another function for parsing date strings. The interface is weird, but if the function happens to suit your application it is just fine. It is problematic to use this function in multi-threaded programs or libraries, since it returns a pointer to a static variable, and uses a global variable and global state (an environment variable).
This variable of type
int contains the error code of the last
unsuccessful call to
getdate. Defined values are:
The environment variable
DATEMSK is not defined or null.
The template file denoted by the
DATEMSK environment variable
cannot be opened.
Information about the template file cannot retrieved.
The template file is not a regular file.
An I/O error occurred while reading the template file.
Not enough memory available to execute the function.
The template file contains no matching template.
The input date is invalid, but would match a template otherwise. This
includes dates like February 31st, and dates which cannot be represented
Preliminary: | MT-Unsafe race:getdate env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | See POSIX Safety Concepts.
The interface to
getdate is the simplest possible for a function
to parse a string and return the value. string is the input
string and the result is returned in a statically-allocated variable.
The details about how the string is processed are hidden from the user.
In fact, they can be outside the control of the program. Which formats
are recognized is controlled by the file named by the environment
DATEMSK. This file should contain
lines of valid format strings which could be passed to
getdate function reads these format strings one after the
other and tries to match the input string. The first line which
completely matches the input string is used.
Elements not initialized through the format string retain the values
present at the time of the
getdate function call.
The formats recognized by
getdate are the same as for
strptime. See above for an explanation. There are only a few
extensions to the
%Zformat is given the broken-down time is based on the current time of the timezone matched, not of the current timezone of the runtime environment.
Note: This is not implemented (currently). The problem is that
time zone abbreviations are not unique. If a fixed time zone is assumed for a
given string (say
EST meaning US East Coast time), then uses for
countries other than the USA will fail. So far we have found no good
solution to this.
tm_wdayvalue the current week’s day is chosen, otherwise the day next week is chosen.
It should be noted that the format in the template file need not only contain format elements. The following is a list of possible format strings (taken from the Unix standard):
%m %A %B %d, %Y %H:%M:%S %A %B %m/%d/%y %I %p %d,%m,%Y %H:%M at %A the %dst of %B in %Y run job at %I %p,%B %dnd %A den %d. %B %Y %H.%M Uhr
As you can see, the template list can contain very specific strings like
run job at %I %p,%B %dnd. Using the above list of templates and
assuming the current time is Mon Sep 22 12:19:47 EDT 1986, we can obtain the
following results for the given input.
|Mon||%a||Mon Sep 22 12:19:47 EDT 1986|
|Sun||%a||Sun Sep 28 12:19:47 EDT 1986|
|Fri||%a||Fri Sep 26 12:19:47 EDT 1986|
|September||%B||Mon Sep 1 12:19:47 EDT 1986|
|January||%B||Thu Jan 1 12:19:47 EST 1987|
|December||%B||Mon Dec 1 12:19:47 EST 1986|
|Sep Mon||%b %a||Mon Sep 1 12:19:47 EDT 1986|
|Jan Fri||%b %a||Fri Jan 2 12:19:47 EST 1987|
|Dec Mon||%b %a||Mon Dec 1 12:19:47 EST 1986|
|Jan Wed 1989||%b %a %Y||Wed Jan 4 12:19:47 EST 1989|
|Fri 9||%a %H||Fri Sep 26 09:00:00 EDT 1986|
|Feb 10:30||%b %H:%S||Sun Feb 1 10:00:30 EST 1987|
|10:30||%H:%M||Tue Sep 23 10:30:00 EDT 1986|
|13:30||%H:%M||Mon Sep 22 13:30:00 EDT 1986|
The return value of the function is a pointer to a static variable of
struct tm, or a null pointer if an error occurred. The
result is only valid until the next
getdate call, making this
function unusable in multi-threaded applications.
errno variable is not changed. Error conditions are
stored in the global variable
getdate_err. See the
description above for a list of the possible error values.
getdate function should never be
used in SUID-programs. The reason is obvious: using the
DATEMSK environment variable you can get the function to open
any arbitrary file and chances are high that with some bogus input
(such as a binary file) the program will crash.
Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | See POSIX Safety Concepts.
getdate_r function is the reentrant counterpart of
getdate. It does not use the global variable
to signal an error, but instead returns an error code. The same error
codes as described in the
getdate_err documentation above are
used, with 0 meaning success.
getdate_r stores the broken-down time in the variable
struct tm pointed to by the second argument, rather than
in a static variable.
This function is not defined in the Unix standard. Nevertheless it is available on some other Unix systems as well.
The warning against using
getdate in SUID-programs applies to
getdate_r as well.