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# tm_yday to time_t?

 P: n/a If I have a year and the day of the year (e.g. yyyy.ddd), is there some simple way to convert this to a time_t? mktime(), of course, does just the opposite and uses tm_mon and tm_mday, ignoring tm_yday. There's the obvious brute force approach of subtracting 31, 28, 31, 30, etc... until you arrive at the right result (being careful to allow for leap years, of course), but it seems like there ought to be some standard library routine for this purpose. It only has to work for "modern" days, post 1970. Thanks, Bob Armstrong Jun 30 '06 #1
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 P: n/a On 30 Jun 2006 15:14:32 -0700, bo*@jfcl.com wrote: If I have a year and the day of the year (e.g. yyyy.ddd), is theresome simple way to convert this to a time_t? mktime(), of course, doesjust the opposite and uses tm_mon and tm_mday, ignoring tm_yday. There's the obvious brute force approach of subtracting 31, 28, 31,30, etc... until you arrive at the right result (being careful to allowfor leap years, of course), but it seems like there ought to be somestandard library routine for this purpose. It only has to work for "modern" days, post 1970. Google for "serial date" or "Julian date". You should find algorithms that can be adapted. I'd say more, but I'm out of here until next Wednesday! -- Al Balmer Sun City, AZ Jun 30 '06 #2

 P: n/a bo*@jfcl.com writes: If I have a year and the day of the year (e.g. yyyy.ddd), is there some simple way to convert this to a time_t? mktime(), of course, does just the opposite and uses tm_mon and tm_mday, ignoring tm_yday. There's the obvious brute force approach of subtracting 31, 28, 31, 30, etc... until you arrive at the right result (being careful to allow for leap years, of course), but it seems like there ought to be some standard library routine for this purpose. It only has to work for "modern" days, post 1970. So, you have the year and the day of the year and you want to get the right year, month and day (or the right time_t value based on those values)? mktime() need a pointer to a struct tm because it modifies it's argument, meaning that it normalizes your date. For example, the following program: #include #include #include int main(void) { struct tm mytm; mytm.tm_year=2006-1900; mytm.tm_mon=0; mytm.tm_mday=365; mytm.tm_isdst=-1; mytm.tm_hour=0; mytm.tm_min=0; mytm.tm_sec=0; if(mktime(&mytm)==-1) { printf("I cannot represent the calendar time :-(\n"); exit(EXIT_FAILURE); } printf("%d\t%d\t%d\n",mytm.tm_year+1900,mytm.tm_mo n,mytm.tm_mday); return 0; } Will output 2006 11 31 (if mktime can represent the time). The values of the 6 fields that matter for mktime (I don't count "dst" here, now) don't have to be in the specified ranges and mktime will change it's argument by setting the components to the correct values. This means that if you say year=106, mon=0 (Jan) mday=32 (1 more than the max number), hour=0, min=0 and sec=0 the values that exceed the ranges will be added (or substracted) to the higher group i.e. mday=32 means 31 day in January + 1 the next month which will make mon=1 and leave everything else unchanged. -- Ioan - Ciprian Tandau tandau _at_ freeshell _dot_ org (hope it's not too late) (... and that it still works...) Jul 1 '06 #3

 P: n/a Nelu wrote: mytm.tm_mday=365; .... That is just extraordinarily clever! And it actually works, too :-) I knew there was some easier way to do it. Thanks, Bob Jul 1 '06 #4

 P: n/a Nelu wrote: bo*@jfcl.com writes: If I have a year and the day of the year (e.g. yyyy.ddd), is there some simple way to convert this to a time_t? mktime(), of course, does just the opposite and uses tm_mon and tm_mday, ignoring tm_yday. There's the obvious brute force approach of subtracting 31, 28, 31, 30, etc... until you arrive at the right result (being careful to allow for leap years, of course), but it seems like there ought to be some standard library routine for this purpose. It only has to work for "modern" days, post 1970. So, you have the year and the day of the year and you want to get the right year, month and day (or the right time_t value based on those values)? mktime() need a pointer to a struct tm because it modifies it's argument, meaning that it normalizes your date. For example, the following program: #include #include #include int main(void) { struct tm mytm; mytm.tm_year=2006-1900; mytm.tm_mon=0; mytm.tm_mday=365; mytm.tm_isdst=-1; mytm.tm_hour=0; mytm.tm_min=0; mytm.tm_sec=0; if(mktime(&mytm)==-1) { printf("I cannot represent the calendar time :-(\n"); exit(EXIT_FAILURE); } printf("%d\t%d\t%d\n",mytm.tm_year+1900,mytm.tm_mo n,mytm.tm_mday); return 0; } Will output 2006 11 31 (if mktime can represent the time). The values of the 6 fields that matter for mktime (I don't count "dst" here, now) don't have to be in the specified ranges and mktime will change it's argument by setting the components to the correct values. This means that if you say year=106, mon=0 (Jan) mday=32 (1 more than the max number), hour=0, min=0 and sec=0 the values that exceed the ranges will be added (or substracted) to the higher group i.e. mday=32 means 31 day in January + 1 the next month which will make mon=1 and leave everything else unchanged. November 31 ? -- Joe Wright "Everything should be made as simple as possible, but not simpler." --- Albert Einstein --- Jul 1 '06 #5

 P: n/a Joe Wright writes: Nelu wrote: bo*@jfcl.com writes: If I have a year and the day of the year (e.g. yyyy.ddd), is there some simple way to convert this to a time_t? mktime(), of course, does just the opposite and uses tm_mon and tm_mday, ignoring tm_yday. There's the obvious brute force approach of subtracting 31, 28, 31, 30, etc... until you arrive at the right result (being careful to allow for leap years, of course), but it seems like there ought to be some standard library routine for this purpose. It only has to work for "modern" days, post 1970. So, you have the year and the day of the year and you want to get the right year, month and day (or the right time_t value based on those values)? mktime() need a pointer to a struct tm because it modifies it's argument, meaning that it normalizes your date. For example, the following program: #include #include #include int main(void) { struct tm mytm; mytm.tm_year=2006-1900; mytm.tm_mon=0; mytm.tm_mday=365; mytm.tm_isdst=-1; mytm.tm_hour=0; mytm.tm_min=0; mytm.tm_sec=0; if(mktime(&mytm)==-1) { printf("I cannot represent the calendar time :-(\n"); exit(EXIT_FAILURE); } printf("%d\t%d\t%d\n",mytm.tm_year+1900,mytm.tm_mo n,mytm.tm_mday); return 0; } Will output 2006 11 31 (if mktime can represent the time). The values of the 6 fields that matter for mktime (I don't count "dst" here, now) don't have to be in the specified ranges and mktime will change it's argument by setting the components to the correct values. This means that if you say year=106, mon=0 (Jan) mday=32 (1 more than the max number), hour=0, min=0 and sec=0 the values that exceed the ranges will be added (or substracted) to the higher group i.e. mday=32 means 31 day in January + 1 the next month which will make mon=1 and leave everything else unchanged. November 31 ? The month is 0 based. (0 - January, 11 - December). I set mytm.tm_mon=0. If you complain about 11 why don't you complain about 0? :-) -- Ioan - Ciprian Tandau tandau _at_ freeshell _dot_ org (hope it's not too late) (... and that it still works...) Jul 1 '06 #6

 P: n/a Nelu writes: Joe Wright writes: Nelu wrote: [snip] November 31 ? The month is 0 based. (0 - January, 11 - December). I set mytm.tm_mon=0. If you complain about 11 why don't you complain about 0? :-) Then again... scratch the last two sentences. Sorry. mday=365 is also out of range for day in month so it could've been interpreted that way for the month, too. I should've put tm_mon+1 instead on tm_mon in printf so it won't lead to confusion. I hope the OP got it right. -- Ioan - Ciprian Tandau tandau _at_ freeshell _dot_ org (hope it's not too late) (... and that it still works...) Jul 1 '06 #7

 P: n/a Nelu wrote: Nelu writes: Joe Wright writes: Nelu wrote: [snip] November 31 ? The month is 0 based. (0 - January, 11 - December). I set mytm.tm_mon=0. If you complain about 11 why don't you complain about 0? :-) Then again... scratch the last two sentences. Sorry. mday=365 is also out of range for day in month so it could've been interpreted that way for the month, too. I should've put tm_mon+1 instead on tm_mon in printf so it won't lead to confusion. I hope the OP got it right. Well, I apologize. tm_mon is indeed 0..11 (12 months) and tm_yday is 0..365 (366 days). -- Joe Wright "Everything should be made as simple as possible, but not simpler." --- Albert Einstein --- Jul 1 '06 #8

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