Talk:Last Friday of each month

command line

Why does the task specify that the year is supplied from the command line? This seems to conflate two totally separate language capabilities--date arithmetic and command line handling. For the PHP example, I'm just ignoring the command line requirement. --Showell 17:37, 20 January 2012 (UTC)

task name

of year? not of month?--eMBee 13:43, 7 November 2011 (UTC)

It looks like it's all of the last fridays of the months of a given year? --Rdm 14:52, 7 November 2011 (UTC)

yes, exactly, which is why i find the current title confusing. something like Last Friday of every month would be more to the point. otherwise, i thought the original title was sufficient. something about fridays. it is clear enough that this is about the calendar. is more details really needed?--eMBee 14:59, 7 November 2011 (UTC)

English is not my born language, but I also find the title "Last Fridays of year" confusing. I understand it as 'really' the last fridays of a given year, for example the last three Fridays of 2012 are 2012-12-14, 2012-12-21 and 2012-12-28. Blue Prawn 21:10, 9 November 2011 (UTC)

exactly my thoughts too. so what's a better title? "last friday of each month?" (i thin kthe fact that it is for a year is less interesting, the same solution would work for any period of time).--eMBee 04:11, 10 November 2011 (UTC)

I'm not particularly attached to the current name; I just thought that the original (“Last Fridays”) wasn't good enough either. Suggested changes are welcome. –Donal Fellows 08:49, 10 November 2011 (UTC)

C version

This discussion is about the program shown here:

<lang c>#define _XOPEN_SOURCE

1. include <stdio.h>
2. include <time.h>

int main(int c, char *v[]) { int days[] = {31,29,31,30,31,30,31,31,30,31,30,31}; int m, y, w; struct tm tm; char buf[32];

if (c < 2 || !sscanf(v[1], "%d", &y)) return 1;

days[1] -= y % 4 || (y % 100 && ! (y % 400)); sprintf(buf, "%d-1-1", y); strptime(buf, "%Y-%m-%d", &tm); w = tm.tm_wday - 1; /* day of week for zeroth of Jan */

for(m = 0; m < 12; m++) { w = (w + days[m]) % 7; printf("%d-%02d-%d\n", y, m + 1, days[m] + (w < 5 ? -2 : 5) - w); }

return 0;

}</lang>

Building the C version under cygwin (gcc 3.4.4), I get:

<lang bash>$ make last_fridays cc last_fridays.c -o last_fridays

$ ./last_fridays 2011 2011-01-27 2011-02-24 2011-03-31 2011-04-28 2011-05-26 2011-06-30 2011-07-28 2011-08-25 2011-09-29 2011-10-27 2011-11-24 2011-12-29

$ ./last_fridays 2012 2012-01-27 2012-02-24 2012-03-30 2012-04-27 2012-05-25 2012-06-29 2012-07-27 2012-08-31 2012-09-28 2012-10-26 2012-11-30 2012-12-28

$ cc --version cc (GCC) 3.4.4 (cygming special, gdc 0.12, using dmd 0.125) Copyright (C) 2004 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.</lang>

The C entry currently shows different results for 2011, but I cannot reproduce them. --Rdm 23:25, 8 November 2011 (UTC)

I'll assume it's a cygwin bug for now. For the record, can you change two lines to

<lang>sprintf(buf, "%d-01-01 09:01:01", y);

strptime(buf, "%Y-%m-%d %H:%M:%S", &tm);</lang> and see how it does? --unsigned

I replaced the sprintf an strptime lines with these two lines and got the same result. Note also that might results are consistent (but this does not prove that the issue is not uninitialized memory). --Rdm 11:17, 9 November 2011 (UTC)

I have a similar problem with OpenBSD 4.9. The output changes from run to run, and might show the last Mondays, Thursdays, Fridays or Saturdays. After the call to strptime(), tm.tm_wday contains junk values like 50237728 or 239567136. (Legal values are 0 to 6.) Change to "%d-01-01 09:01:01" and "%Y-%m-%d %H:%M:%S" is no help. Checking my manuals, mktime(3) describes the fields of struct tm, but strptime(3) is vague; I assume that strptime() never fills tm_wday unless the string contains the weekday. --Kernigh 01:05, 9 November 2011 (UTC)