[SOLVED] Getting text between two points in C.

anon02 · 10-25-2011, 10:49 AM

With Christmas in about 2 months, I have decided to modify my game, The Crimson Swarm, for a more christmassy version. Every day, the player will be given a new starter item, however I need to find the day. I have got it to print the time like;

Code:

Tue Oct 25 16:34:10 2011

However I want it to get 'Oct' and '25' from that char. I have searched the web for something which works like:

Code:

strcpy(c,function_name(time_string,4,7));

Which would set c to be Oct, and so on.
Are there any functions like that?

Also, is there a way to convert a char * to a int, for easier comparison.

Also, can anyone give me any pointers on how to save things to files, I know how to output them, but how could I make a folder in the home/user directory named '.christmasswarm' which has the files in?

tronayne · 10-25-2011, 11:13 AM

If you do something along these lines

Code:

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

void    main    (void)
{
        time_t  now;
        struct  tm      *tm;

        (void) time (&now);
        tm = localtime (&now);
        /*      show a two-digit year           */
        (void) fprintf (stdout, "Today is %02d/%02d/%02d\n",                                        
            tm->tm_mon+1, tm->tm_mday, tm->tm_year % 100);                                          
        /*      show a four-digit year          */                                                  
        (void) fprintf (stdout, "Today is %02d/%02d/%d\n",                                          
            tm->tm_mon+1, tm->tm_mday, tm->tm_year + 1900);                                         
        exit (EXIT_SUCCESS);
}

See how the tm structure elements are used? And, of course, you can use them in a if.

time.h has these structure elements:

Code:

struct tm
{
  int tm_sec;                   /* Seconds.     [0-60] (1 leap second) */
  int tm_min;                   /* Minutes.     [0-59] */
  int tm_hour;                  /* Hours.       [0-23] */
  int tm_mday;                  /* Day.         [1-31] */
  int tm_mon;                   /* Month.       [0-11] */
  int tm_year;                  /* Year - 1900.  */
  int tm_wday;                  /* Day of week. [0-6] */
  int tm_yday;                  /* Days in year.[0-365] */
  int tm_isdst;                 /* DST.         [-1/0/1]*/
};

So, if you follow the above example, you are going to get numeric values you can use for your purposes.

Hope this helps some.

anon02 · 10-25-2011, 11:20 AM

Perfect. I am going to add that to the code once I have made a few tests with it, but it should be fine. Thanks!

anon02 · 10-25-2011, 12:09 PM

Hmm... I tried setting two variables to be the date, however it errors:

Code:

void twelvedays(void)
{
        time_t  now;
        struct  tm      *tm;





        time (&now);
        tm = localtime (&now);
	month = tm->tm_mon+1;
	day = tm->tm_mday;

Is the code, and lines 161, 162, and 163:

Code:

     tm = localtime (&now);
	month = tm->tm_mon+1;
	day = tm->tm_mday

error with:

Code:

main.c:161:12: warning: assignment makes pointer from integer without a cast [enabled by default]
main.c:162:12: error: dereferencing pointer to incomplete type
main.c:163:10: error: dereferencing pointer to incomplete type

Which probably means I need something like 'int' or 'char', yet the example you gave did not have that, yet I can see no other reasons for it to fail. Any ideas?

NevemTeve · 10-25-2011, 12:38 PM

#include <time.h>

for a start

anon02 · 10-25-2011, 12:48 PM

Quote:

Originally Posted by NevemTeve

#include <time.h>

for a start

Ah, even though I had not put any of the other code, you still worked out that one. Works fine as rain now! Thanks!

tronayne · 10-25-2011, 01:50 PM

You might be going at it kind of sorta not quite what you want.

The tm structure elements are filled in by the call to localtime (&now) where now is the number of seconds from the epoch (00:00:00 01 Jan 1970). You only need to invoke tm = time (&now); once in your program (you're working with days, not seconds). So,

Code:

time_t  now;
struct  tm      *tm;

/*     get the system time in seconds from the epoch     */
(void) time (&now);
/*     convert that to local time                        */
tm = localtime (&now);

You'd only do that one time in a running program.

So, I think what you're trying to do is add a day (then another and another and so on) and use the tm structure?

OK, so here's a trick. A day is 86,400 seconds. Tomorrow is the value of now + 86,400. So

Code:

/*     what's tomorrow?                                 */
now += (time_t) 86400;
/*     fill the tm structure with tomorrow       */
localtime (&now);

and then use those values as you see fit (cute, eh?). The localtime() utility takes care of all the calendar changes (so, if somebody was running on 31 October and we add one day the tm structure will contain values for 01 November. Similarly, if you added five days (86400*5), you'd get a correct rollover at the end of a month, irrespective of what month it may be.

I didn't answer part of your question about writing to a file in the user's home directory.

All you'd need to do is a quick-and-dirty write of the value of now in a file, say a "dot" file so it's not readily visible to the user, something like .timestamp, something like this

Code:

time_t  now, oldtime;
struct  tm      *tm;
FILE    *out;

/*      get the current system time                             */
(void) time (&now);
/*      fill the tm structure elements                          */
tm = localtime (&now);
/*      initialize old timestamp                                */
oldtime = (time_t) 0;
/*      try to read an existing file                            */
if ((out = fopen (".timestamp", "r")) != (FILE *) NULL) {
        /*      it exists, read the value in it                 */
        (void) fscanf (out, "%ld\n", &oldtime);
        (void) fclose (out);
}
/*
        now, simply open it for writing (which clears the
        existing content) and put the current time stamp into it
*/
if ((out = fopen (".timestamp", "w")) == (FILE *) NULL) {
        /*      just in case there's a problem                  */
        (void) fprintf (stderr,
            "%s:\tcan't create %s\n",
            argv [0], ".timestamp");
        exit (EXIT_FAILURE);
}
/*      write the current time to the file              */
(void) fprintf (out, "%ld\n", now);
(void) fclsoe (out);
/*
 *      you can do whatever arithmetic you need to on the
 *      values of oldtime and now, just keep in mind that
 *      the difference between the two is what you need to
 *      work with and that oldtime will possibly be a few
 *      minutes ago, yesterday, a week ago or whatever and
 *      code appropriately to deal with that
*/

Hope this helps some.

anon02 · 10-25-2011, 01:58 PM

Thanks for the tip. Now I have got it working (Or I think so, it counts 25 days and I have only tested it today. I am going to have November as testing month so I have 5 days now to add stuff, and 5 days after before release).