Thread: For Loop leaves C-String untouched

What about this?

Code:

#define _XOPEN_SOURCE
#include <stdio.h>
#include <time.h>

char *time_conversion( char *t )
{
  static char s[9];
  struct tm tm;

  strptime( t, "%I:%M:%S %p", &tm ); 

  // this "format" (4th argument) is glibc's only!
  // use "%H:%M:%S" in other compilers...
  if ( strftime( s, sizeof s, "%02H:%02M:%02S", &tm ) )
    return s;

  // return NULL in case of "error".
  return NULL;
}

int main( void )
{
  char *s = "7:23:00 PM"; // test.

  printf( "'%s' -> '%s'\n", s, time_conversion( s ) );  
}

Sorry... it doen't work as you expected... Here's another implementation:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
// requires a string formated as:
//    "[h]h:mm[:ss][ am/pm]"
char *time_conversion( char *t )
{
  static char s[9];
  char *p, *q;
  int step = 0;
  int hr, m, sec = 0;
 
  *s = '\0';

  // make a copy...
  p = strdup( t );

  q = strtok( p, ": " );
  while ( q )
  {
    switch ( step++ )
    {
      case 0:   // hour.
        hr = atoi(q); break;
      case 1:   // minuttes
        m = atoi(q); break;
      case 2: // seconds or AM/PM.
      case 3:
        if ( ! strcasecmp( q , "PM" ) )
        {
          if ( hr < 12 )
            hr += 12;
          break;
        }

        if ( ! strcasecmp( q, "AM" ) )
        {
          if ( hr == 12 )
            hr = 0;
          break;
        }

        sec = atoi(q);
        break;

      // ignore everything else...
      default:
        goto exit_loop;
    }

    q = strtok(NULL, ": " );
  }

exit_loop:
  free( p );

  sprintf( s, "%02d:%02d:%02d", hr, m, sec );
 
  return s;
}
 
int main( void )
{
  char *s[] = { "0:00", "12:00 AM", "11:59:59 AM", "10:23", "12:00", "12:00:00 PM", "7:23 PM", "8:01:03 PM", NULL }; // tests.
  char **p;
 
  p = s;
  while ( *p )
  {
    printf( "%-13s -> %s\n", *p, time_conversion( *p ) );  
    p++;
  }
}

Testing:

Code:

$ cc -o test test.c
$ ./test
0:00          -> 00:00:00
12:00 AM      -> 00:00:00
11:59:59 AM   -> 11:59:59
10:23         -> 10:23:00
12:00         -> 12:00:00
12:00:00 PM   -> 12:00:00
7:23 PM       -> 19:23:00
8:01:03 PM    -> 20:01:03