stuck on time_t

[Jim Showalter]

I want to get the current date/time using time(), then use ctime() to
display it.

What type is time_t? I've tried looking it up in time.h and elsewhere.
"grep" shows: typedef __time_t time_t;

which, in turn, greps as: __time_t tv_sec;

Here's my latest attempt:


#include <stdio.h>
#include <stdlib.h>
#include <time.h>


int
main (void)
{
time_t eot, *tod;

eot = time(tod);
printf("*tod\t = %ul\n", *tod);
printf("Today's date is: %s\n", ctime(tod));

return EXIT_SUCCESS;
}


What am I doing wrong?

Also, how can I determine the max value time_t can hold?


jim

--
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
_/ Everything should be made as simple as possible, but not simpler.
_/ -- Albert Einstein
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/

[Emmanuel Delahaye]

Re: stuck on time_t

Jim Showalter wrote on 08/08/04 :[color=blue]
> I want to get the current date/time using time(), then use ctime() to
> display it.
>
> What type is time_t?[/color]

It's time_t. You don't need to know more except that it could be a
floating point.
[color=blue]
> #include <stdio.h>
> #include <stdlib.h>
> #include <time.h>
>
> int
> main (void)
> {
> time_t eot, *tod;
>
> eot = time(tod);[/color]

Wrong. You are passing an undefined value to a function. My compiler
chokes on that. Yours should if it has been correctly configured.

eot = time (NULL);

or

time (&eot);

get rid of this tod. It's useless.
[color=blue]
> printf("*tod\t = %ul\n", *tod);
> printf("Today's date is: %s\n", ctime(tod));[/color]

printf("*tod\t = %ul\n", (unsigned long) eot);
printf("Today's date is: %s\n", ctime(eot));
[color=blue]
> return EXIT_SUCCESS;
> }[/color]

Note that ctime() returns the adress of a static string. It may behave
strangely if you don't make a copy of the pointed string. Better to use
strftime() (and it's more fun, actually).

--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html

"C is a sharp tool"

[Jim Showalter]

Re: stuck on time_t

Emmanuel Delahaye wrote:
[color=blue]
> Jim Showalter wrote on 08/08/04 :[color=green]
>> I want to get the current date/time using time(), then use ctime() to
>> display it.
>>
>> What type is time_t?[/color]
>
> It's time_t. You don't need to know more except that it could be a
> floating point.
>
> Note that ctime() returns the adress of a static string. It may behave
> strangely if you don't make a copy of the pointed string. Better to use
> strftime() (and it's more fun, actually).
>[/color]

Ok, I got it working - thanks Emmanuel! But you missed my other
question at the end, which was: How can I determine the max value
time_t can hold?


jim
--
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
_/ Everything should be made as simple as possible, but not simpler.
_/ -- Albert Einstein
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/

[SM Ryan]

Re: stuck on time_t

# Ok, I got it working - thanks Emmanuel! But you missed my other
# question at the end, which was: How can I determine the max value
# time_t can hold?

System dependent. On current unices it's good to about 2039. Mac Classic
is until 2104 I think, perhaps. Windows clocks are good until 2003. Or
8:03 PM if you prefer that notation. If you have a choice, don't store
time_t in a file, but use something like ISO calendar values. Hopefully
the time_t value will change to 64 bits before 2039.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
The little stoner's got a point.

[Jim Showalter]

Re: stuck on time_t

SM Ryan wrote:
[color=blue]
> # Ok, I got it working - thanks Emmanuel! But you missed my other
> # question at the end, which was: How can I determine the max value
> # time_t can hold?
>
> System dependent. On current unices it's good to about 2039. Mac Classic
> is until 2104 I think, perhaps. Windows clocks are good until 2003. Or
> 8:03 PM if you prefer that notation. If you have a choice, don't store
> time_t in a file, but use something like ISO calendar values. Hopefully
> the time_t value will change to 64 bits before 2039.
>
> --
> SM Ryan http://www.rawbw.com/~wyrmwif/
> The little stoner's got a point.[/color]

2003? Glad I'm not programming on Windows! :)

Seriously, that's about what I figured - but not my concern. I'm just
trying to complete the first "Programmin g Challenge" in Peter van der
Linden's book, "Expert C Programming", and I'm already stumped!

Surely there is a method using C to determine the greatest value that
any type can hold?


jim
--
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
_/ Everything should be made as simple as possible, but not simpler.
_/ -- Albert Einstein
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/

[SM Ryan]

Re: stuck on time_t

# Surely there is a method using C to determine the greatest value that
# any type can hold?

sizeof(T)*CHAR_ BIT will usually be the number of bits, but doesn't say
anything about how the value is encoded in the bits.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
GERBILS
GERBILS
GERBILS

[CBFalconer]

Re: stuck on time_t

Jim Showalter wrote:[color=blue]
>[/color]
.... snip ...[color=blue]
>
> Surely there is a method using C to determine the greatest value
> that any type can hold?[/color]

#include <limits.h>
#include <float.h>

--
Chuck F (cbfalconer@yah oo.com) (cbfalconer@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!

[Joe Wright]

Re: stuck on time_t

Emmanuel Delahaye wrote:
[color=blue]
> Jim Showalter wrote on 08/08/04 :
>[color=green]
>> I want to get the current date/time using time(), then use ctime() to
>> display it.
>>
>> What type is time_t?[/color]
>
>
> It's time_t. You don't need to know more except that it could be a
> floating point.
>[color=green]
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <time.h>
>>
>> int
>> main (void)
>> {
>> time_t eot, *tod;
>>
>> eot = time(tod);[/color]
>
>
> Wrong. You are passing an undefined value to a function. My compiler
> chokes on that. Yours should if it has been correctly configured.
>
> eot = time (NULL);
>
> or
>
> time (&eot);
>
> get rid of this tod. It's useless.
>[color=green]
>> printf("*tod\t = %ul\n", *tod);
>> printf("Today's date is: %s\n", ctime(tod));[/color]
>
>
> printf("*tod\t = %ul\n", (unsigned long) eot);
> printf("Today's date is: %s\n", ctime(eot));
>[color=green]
>> return EXIT_SUCCESS;
>> }[/color]
>
>
> Note that ctime() returns the adress of a static string. It may behave
> strangely if you don't make a copy of the pointed string. Better to use
> strftime() (and it's more fun, actually).[/color]

time.h on my system prototypes ...

char * ctime(const time_t *_cal);

.... indicating that ctime() wants a pointer, ctime(&eot) in your
example. No?

--
Joe Wright mailto:joewwrig ht@comcast.net
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Emmanuel Delahaye]

Re: stuck on time_t

Joe Wright wrote on 08/08/04 :[color=blue][color=green]
>> printf("Today's date is: %s\n", ctime(eot));[/color]
>
> char * ctime(const time_t *_cal);
>
> ... indicating that ctime() wants a pointer, ctime(&eot) in your example. No?[/color]

Yes, I meant:

printf("Today's date is: %s\n", ctime(&eot));

thanks for the correction.

--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html

"C is a sharp tool"