I have an unusual posting style where I tend to waste the first paragraph of a post. Newsreading requires a news writer, and any writer worth his salt does not approach his topic too quickly.
So it is that I might ask for the answer before I have the subject or keywords that might power an internet browser search with some degree of relevance.
Jacob was talking about ISO changing definitions of time. The only c version of computer time I had dealt with was difftime(), and the appropriate call of type time_t that seeds srand().
The background reading in H&S reveals *several* C time facilties, and I want to work my way through them all at least once for kicks and giggles.
What I want now is a means to date my construction bids. Their form is to be: November 7, 2008
How might I best achieve that? -- frank
"Rape: is it too much to ask for corporations who bid on federal contracts to refrain from?"
On 8 Nov, 03:03, frank <fr...@example.invalid> wrote:
> I have an unusual posting style where I tend to waste the first paragraph > of a post. Newsreading requires a news writer, and any writer worth his > salt does not approach his topic too quickly.
we've got to find something to do with all that Dark Fibre
<snip>
> Jacob was talking about ISO changing definitions of time.
bloody hell I never new ISO had such powers. So is time going to go faster or slower? Or just hopabout at random?
Jacob, was actually talking about the tightening up of the definition of a particular function named asctime().
> The only c > version of computer time I had dealt with was difftime(),
This is what I'd call a type error (apparently the officila name is a Category Error). difftime() is a function it is not a "version" of time.
> and the > appropriate call of type time_t that seeds srand().
time_t is a type or type alias. It cannot be called.
> The background reading in H&S reveals *several* C time facilties, and I > want to work my way through them all at least once for kicks and giggles.
ok
> What I want now is a means to date my construction bids. Their form is > to be: > November 7, 2008
> How might I best achieve that?
take a look at strftime(). Or even sprintf(). If you can avoid a format like this. There is less ambiguity and its easier for automatic processing if you use the international standard ISO-8601 2008-11-07
Nick Keighley wrote: > On 8 Nov, 03:03, frank <fr...@example.invalid> wrote:
>> I have an unusual posting style where I tend to waste the first paragraph >> of a post. Newsreading requires a news writer, and any writer worth his >> salt does not approach his topic too quickly.
> we've got to find something to do with all that Dark Fibre
> <snip>
>> Jacob was talking about ISO changing definitions of time.
> bloody hell I never new ISO had such powers. So is time going to go > faster or slower? Or just hopabout at random?
> Jacob, was actually talking about the tightening up of the definition > of a particular function named asctime().
>> The only c >> version of computer time I had dealt with was difftime(),
> This is what I'd call a type error (apparently the officila name is a > Category Error). difftime() is a function it is not a "version" of > time.
>> and the >> appropriate call of type time_t that seeds srand().
> time_t is a type or type alias. It cannot be called.
>> The background reading in H&S reveals *several* C time facilties, and I >> want to work my way through them all at least once for kicks and giggles.
> ok
>> What I want now is a means to date my construction bids. Their form is >> to be: >> November 7, 2008
>> How might I best achieve that?
> take a look at strftime(). Or even sprintf(). If you can avoid a > format like this. There is less ambiguity and its easier for automatic > processing if you use the international standard ISO-8601 2008-11-07
It is indeed a great idea. Extend it some by adding time to date:
"2009-11-08 11:12:31"
Now you have a string which can be sorted lexically with strcmp(). -- Joe Wright "If you rob Peter to pay Paul you can depend on the support of Paul."
On Sun, 08 Nov 2009 05:40:21 -0800, Nick Keighley wrote: > On 8 Nov, 03:03, frank <fr...@example.invalid> wrote: >> Jacob was talking about ISO changing definitions of time.
> bloody hell I never new ISO had such powers. So is time going to go > faster or slower? Or just hopabout at random?
> Jacob, was actually talking about the tightening up of the definition of > a particular function named asctime().
Yeah. Somehow I had the errant notion that standard C had only difftime () to offer. I'll see if I can find that other thread and read more.
>> The only c >> version of computer time I had dealt with was difftime(),
> This is what I'd call a type error (apparently the officila name is a > Category Error). difftime() is a function it is not a "version" of time.
>> and the >> appropriate call of type time_t that seeds srand().
> time_t is a type or type alias. It cannot be called.
>> The background reading in H&S reveals *several* C time facilties, and I >> want to work my way through them all at least once for kicks and >> giggles.
> ok
Well it's not too hard to get on the scoreboard here:
dan@dan-desktop:~/source$ cat time1.c
#include <stdio.h> #include <time.h>
int main(void) { time_t now; now = time(NULL); printf ("The current date and time is: %s\n", ctime(&now)); return 0;
}
// gcc -Wall -Wextra time1.c -o out dan@dan-desktop:~/source$ gcc -Wall -Wextra time1.c -o out dan@dan-desktop:~/source$ ./out The current date and time is: Mon Nov 9 00:10:24 2009
dan@dan-desktop:~/source$
I faltered on two further attempts, one using unix extensions and another using localtime. I can rarely cook from scratch with structs and no help:
my_time = localtime(&now); printf ("The current date and time is: \n" ); return 0;
}
// gcc -Wall -Wextra time3.c -o out
dan@dan-desktop:~/source$ gcc -Wall -Wextra time3.c -o out time3.c: In function ‘main’: time3.c:11: error: ‘tm’ undeclared (first use in this function) time3.c:11: error: (Each undeclared identifier is reported only once time3.c:11: error: for each function it appears in.) time3.c:11: error: expected ‘;’ before ‘my_time’ time3.c:13: error: ‘my_time’ undeclared (first use in this function) dan@dan-desktop:~/source$
>> What I want now is a means to date my construction bids. Their form is >> to be: >> November 7, 2008
>> How might I best achieve that?
> take a look at strftime(). Or even sprintf(). If you can avoid a format > like this. There is less ambiguity and its easier for automatic > processing if you use the international standard ISO-8601 2008-11-07
P. 448 has this for the synopsis but the explanation is too much for me :( size_t strftime( char * s, size_t maxsize, const char *format, const struct tm *timeptr);
> Yeah. Somehow I had the errant notion that standard C had only difftime > () to offer. I'll see if I can find that other thread and read more.
I don't know what you mean by "had only difftime() to offer". Standard C has a number of other functions that deal with time. See the standard or any decent C reference for details.
localtime is declared for you in <time.h>. Redeclaring is either illegal (if you get it wrong) or useless (if you get it right).
> now = time(NULL); > tm my_time;
The type is called "struct tm", not "tm".
> my_time = localtime(&now);
If you declare my_time as "struct tm my_time;", this is illegal; localtime returns a struct tm*, not a struct tm.
If you change the declaration to "struct tm *my_time;", it should compile.
> printf ("The current date and time is: \n" );
Ok, what are you trying to do here?
And *please* indent your code.
> return 0; > }
[...]
> P. 448 has this for the synopsis but the explanation is too much for me :( > size_t strftime( > char * s, size_t maxsize, > const char *format, > const struct tm *timeptr);
Perhaps this example will help:
#include <stdio.h> #include <time.h> int main(void) { const time_t now = time(NULL); const struct tm *ltime = localtime(&now); char buf[100]; const size_t result = strftime(buf, sizeof buf, "%a %Y-%m-%d %H:%M:%S %Z", ltime); printf("strftime() returned %u\n", (unsigned)result); printf("It is now %s\n", buf); return 0;
}
-- Keith Thompson (The_Other_Keith) ks...@mib.org <http://www.ghoti.net/~kst> Nokia "We must do something. This is something. Therefore, we must do this." -- Antony Jay and Jonathan Lynn, "Yes Minister"
On 8 Nov, 16:30, Joe Wright <joewwri...@comcast.net> wrote:
> Nick Keighley wrote: > > On 8 Nov, 03:03, frank <fr...@example.invalid> wrote:
<snip>
> >> What I want now is a means to date my construction bids. Their form is > >> to be: > >> November 7, 2008
> >> How might I best achieve that?
> > take a look at strftime(). Or even sprintf(). If you can avoid a > > format like this. There is less ambiguity and its easier for automatic > > processing if you use the international standard ISO-8601 2008-11-07
> It is indeed a great idea. Extend it some by adding time to date:
> "2009-11-08 11:12:31"
maybe he doesn't have the time of day available. ISO 8601 allows my version as well. Are construction bids noramlly timed to the second? Why did you omit the time zone and Daylight Saving Time?
> Now you have a string which can be sorted lexically with strcmp().
why couldn't my version be sorted lexically with strcmp()?
On 9 Nov, 07:24, frank <fr...@example.invalid> wrote:
> On Sun, 08 Nov 2009 05:40:21 -0800, Nick Keighley wrote: > > On 8 Nov, 03:03, frank <fr...@example.invalid> wrote: > >> Jacob was talking about ISO changing definitions of time. [...] > > Jacob, was actually talking about the tightening up of the definition of > > a particular function named asctime().
> Yeah. Somehow I had the errant notion that standard C had only difftime > () to offer. I'll see if I can find that other thread and read more.
Standard C has a collection of time related functions. Lookup the header time.h. This site is not bad:-
> >> The background reading in H&S reveals *several* C time facilties, and I > >> want to work my way through them all at least once for kicks and > >> giggles.
<snip>
> I faltered on two further attempts, one using unix extensions
I'd steer away from these initially
> and another > using localtime. I can rarely cook from scratch with structs and no help:
if you're on unix then try the man pages. That dinkumware link I posted is ok. Do you have a book, like K&R?
don't do this. time.h will define localtime(), so you are either getting the definition wrong or repeating something unnecessarily. Let the standard headers define function prototypes etc.
> now = time(NULL);
you are mixing declarations with statements which isn't allowed in C89. Move the call to time() so it appears after the decalarations.
> tm my_time;
you mean
struct tm *my_time;
C insists on the struct keyword being there (which is why I typedef my structs) and localtime returns a pointer to a struct tm.
> my_time = localtime(&now); > printf ("The current date and time is: \n" ); > return 0;
> }
> // gcc -Wall -Wextra time3.c -o out
> dan@dan-desktop:~/source$ gcc -Wall -Wextra time3.c -o out > time3.c: In function ‘main’: > time3.c:11: error: ‘tm’ undeclared (first use in this function) > time3.c:11: error: (Each undeclared identifier is reported only once > time3.c:11: error: for each function it appears in.) > time3.c:11: error: expected ‘;’ before ‘my_time’ > time3.c:13: error: ‘my_time’ undeclared (first use in this function) > dan@dan-desktop:~/source$
> >> What I want now is a means to date my construction bids. Their form is > >> to be: > >> November 7, 2008
> >> How might I best achieve that?
> > take a look at strftime(). Or even sprintf(). If you can avoid a format > > like this. There is less ambiguity and its easier for automatic > > processing if you use the international standard ISO-8601 2008-11-07
> P. 448
of H&S? I always consideredd that H&S was pretty good on the library. Still I've given you several other references.
> has this for the synopsis but the explanation is too much for me :( > size_t strftime( > char * s, size_t maxsize, > const char *format, > const struct tm *timeptr);
it's a bit like sprintf() you give it a time and it produces a string representing the time in a format you describe. I don't find the format options very intuitive so I often use sprintf() instead.
On Mon, 09 Nov 2009 00:17:18 -0800, Keith Thompson wrote: > frank <fr...@example.invalid> writes: [...] >> Yeah. Somehow I had the errant notion that standard C had only >> difftime () to offer. I'll see if I can find that other thread and >> read more.
> I don't know what you mean by "had only difftime() to offer". Standard C > has a number of other functions that deal with time. See the standard > or any decent C reference for details.
What's funny is that I came up with this notion reading your comments. I was pretty wet behind the ears back then. I'm certain the error was in my partial understanding.
> If you change the declaration to "struct tm *my_time;", it should > compile.
>> printf ("The current date and time is: \n" );
> Ok, what are you trying to do here?
> And *please* indent your code.
I get farther with this on two fronts. The struct declaration is legal, but I still can't get the syntax right to see some output. *Plus*, it took me one minute to install indent:
time3.c: In function ‘main’: time3.c:13: error: request for member ‘tm_day’ in something not a structure or union dan@dan-desktop:~/source$ cat time3.c
#include <stdio.h> #include <time.h>
int main(void) { time_t now; struct tm *localtime(const time_t *t ); now = time(NULL); struct tm *my_time;
my_time = localtime(&now); printf ("The current day is: %s\n", my_time.tm_day ); return 0;
int main (void) { time_t now; struct tm *localtime (const time_t * t); now = time (NULL); struct tm *my_time;
my_time = localtime (&now); printf ("The current day is: %s\n", my_time.tm_day); return 0;
}
// gcc -Wall -Wextra time3.c -o out
> Perhaps this example will help:
dan@dan-desktop:~/source$ cat time4.c
#include <stdio.h> #include <time.h> int main(void) { const time_t now = time(NULL); const struct tm *ltime = localtime(&now); char buf[100]; const size_t result = strftime(buf, sizeof buf, "%a %Y-%m-%d %H:%M:%S %Z", ltime); printf("strftime() returned %u\n", (unsigned)result); printf("It is now %s\n", buf); return 0;
}
// gcc -Wall -Wextra time4.c -o out dan@dan-desktop:~/source$ gcc -Wall -Wextra time4.c -o out dan@dan-desktop:~/source$ ./out strftime() returned 27 It is now Mon 2009-11-09 02:19:21 MST dan@dan-desktop:~/source$
Thx, Keith. I'll see if I can wrap my head around this. -- frank
On 9 Nov, 09:28, frank <fr...@example.invalid> wrote:
> On Mon, 09 Nov 2009 00:17:18 -0800, Keith Thompson wrote: > > frank <fr...@example.invalid> writes:
<snip>
> > If you change the declaration to "struct tm *my_time;", it should > > compile.
> >> printf ("The current date and time is: \n" );
> > Ok, what are you trying to do here?
> > And *please* indent your code.
> I get farther with this on two fronts. The struct declaration is legal, > but I still can't get the syntax right to see some output. *Plus*, it > took me one minute to install indent:
a program as small as that could have been indented "by hand". It's really a good idea to get into the habbit of laying it out nicely as you type it in.
> time3.c: In function ‘main’: > time3.c:13: error: request for member ‘tm_day’ in something not a > structure or union
what is the type of my_time? Is it a structure (struct) or union? [clue: "no"]. What type is tm_day? Is it a C string? It pays to read the documentaion you have carefully.
<snip>
> struct tm *my_time; > [...] > printf ("The current day is: %s\n", my_time.tm_day );
Nick Keighley wrote: > On 8 Nov, 16:30, Joe Wright <joewwri...@comcast.net> wrote: >> Nick Keighley wrote: >>> On 8 Nov, 03:03, frank <fr...@example.invalid> wrote:
> <snip>
>>>> What I want now is a means to date my construction bids. Their form is >>>> to be: >>>> November 7, 2008 >>>> How might I best achieve that? >>> take a look at strftime(). Or even sprintf(). If you can avoid a >>> format like this. There is less ambiguity and its easier for automatic >>> processing if you use the international standard ISO-8601 2008-11-07 >> It is indeed a great idea. Extend it some by adding time to date:
>> "2009-11-08 11:12:31"
> maybe he doesn't have the time of day available. ISO 8601 allows my > version as well. Are construction bids noramlly timed to the second? > Why did you omit the time zone and Daylight Saving Time?
>> Now you have a string which can be sorted lexically with strcmp().
> why couldn't my version be sorted lexically with strcmp()?
I wasn't correcting you in any way. I was being supportive of your suggestion. -- Joe Wright "If you rob Peter to pay Paul you can depend on the support of Paul."
On Mon, 09 Nov 2009 00:40:59 -0800, Nick Keighley wrote: >> struct tm *localtime(const time_t *t );
> don't do this. time.h will define localtime(), so you are either getting > the definition wrong or repeating something unnecessarily. Let the > standard headers define function prototypes etc.
ok
>> now = time(NULL);
> you are mixing declarations with statements which isn't allowed in C89. > Move the call to time() so it appears after the decalarations.
I thought it wasn't allowed in C99. [snip] I think I have something that looks right now.
// gcc -Wall -Wextra time6.c -o out dan@dan-desktop:~/source$
(Code review requested.) It is a singular pleasure to code C on linux.
>> I faltered on two further attempts, one using unix extensions
> I'd steer away from these initially.
But that's where I want to go. Doing time on *nix with C sounds like a great way for me to get my feet wet. I'll x-post to comp.unix.programmer and set the follow-up to there as well.
P. 444 of H&S V shows the unix version of this material as #include <sys/types.h> #include <sys/times.h> ...
times.h wasn't too tough to read. What does types.h have of relevance to getting the time from the OS?
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