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/************************************************************************
*
* Purpose: By default, display yesterdays date.
* If a number is given on the command line, it is subtracted
* from todays date and the result printed.
*
* Author: M.J. Leslie.
*
* Date: 10-Jan-95
*
************************************************************************/
#include <time.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#define DAYS 1
/* Validate the command line
* parmeters */
int check_parm(int argc, char *argv[]);
/************************************************************************/
main(int argc, char *argv[])
{
time_t seconds;
const int one_day = 86400; /* Number of seconds in a day */
int days=DAYS; /* Number of days to subtract. */
/* Checkout the cmd line parms */
if (check_parm( argc, argv))
{
/* Data is OK.
* Override the default. */
days = atoi(argv[1]);
}
/* Get current calendar time.
* This is the number of seconds
* since 1-jan-1970 */
time(&seconds);
/* Subtract the required number
* of days. */
seconds -= one_day*days;
/* Return the required date. */
printf("%s", ctime(&seconds));
/* All done - time to go home. */
exit(1);
}
/************************************************************************
*
* Validate the data enter on the command line.
*
************************************************************************/
int check_parm(int argc, char *argv[])
{
if (argc > 1 ) /* Q. Have we got parms? */
{
if ( !strcmp("-h", argv[1])) /* Q. Help requested? */
{
/* Y. */
printf("%s will return the date of a passed day.", argv[0]);
puts("\nFor example:");
printf("\t%s \tReturns yesterdays date.\n", argv[0]);
printf("\t%s 1 \tReturns yesterdays date.\n", argv[0]);
printf("\t%s 365\tReturns the date one year ago.\n\n", argv[0]);
exit(0);
}
/* Do a simple check to validate
* the I/P data - not 100% reliable
*/
if (!isdigit(*argv[1]))
{
/* Data naff.
* End the program. */
printf("%s: Numeric value required.\n", argv[0]);
printf("\n\tTry: %s -h for some info.\n\n", argv[0]);
exit(0);
}
return(1);
}
return(0);
}
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