2.文件IO---time（打印当地时间）

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《Makefile》

CC=gcc
TEXT=time
SVC=file_time.c debug.h
$(TEXT): $(SVC)
$(CC) -o $@ $^
clean:
rm -rf $(TEXT) *.o
*************************

《头文件》

/*Comment/uncomment the following line to disable/enable debugging,
OR define(or NOT) it in Makefile.
*/
//#define NDEBUG

#undef pr_debug /* undef it, just in case */

#ifndef NDEBUG
#ifdef __KERNEL__
     /* This one if debugging is on, and kernel space */
  #define pr_debug(fmt, args...) printk( KERN_ERR fmt, ## args)
#else
    /* This one for user space */
  #define pr_debug(fmt, args...) fprintf(stderr, fmt, ## args)
#endif
#else
#define pr_debug(fmt, args...) /* not debugging: nothing */
#endif

*************************

/* usage example: ./file_time test.txt */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <time.h>

#include "debug.h"

void usage (const char *s)
{
printf("usage:\n\t%s time_file\n", s);
}
int main(int argc, char **argv)
{

FILE *fp = NULL;
time_t seconds;
struct tm *pTime = NULL;
char buf[BUFSIZ];
int i = 0;

if(argc != 2) {
  usage(argv[0]);
  exit(1);
}

fp = fopen(argv[1], "a+");

assert(fp != NULL);
if (!fp ) {
  usage(argv[0]);
  exit(1);
}

fseek(fp, 0, SEEK_SET); //rewind(fp);

while(!feof(fp)) {
  fgets(buf, BUFSIZ,fp);
  if (buf[0] != EOF)
   ++i;
}

pr_debug("i =%d \n", i);

while(1) {
  seconds = time (NULL);
  pTime = localtime(&seconds);
  assert(pTime);

  sprintf(buf, "%d. %d-%d-%d %d:%d:%d\n", i++, pTime->tm_year+1900, pTime->tm_mon, pTime->tm_mday,
     pTime->tm_hour, pTime->tm_min, pTime->tm_sec);

  pr_debug("%s\n", buf);
  fwrite(buf, strlen(buf), 1, fp);
  fflush(fp);

  sleep(1);

}
fclose(fp);

return 0;
}

***************

执行方式：./ time file_time

结果：

i =1
1. 2011-11-7 17:50:34

2. 2011-11-7 17:50:35

3. 2011-11-7 17:50:36

4. 2011-11-7 17:50:37

5. 2011-11-7 17:50:38

6. 2011-11-7 17:50:39

7. 2011-11-7 17:50:40

8. 2011-11-7 17:50:41

9. 2011-11-7 17:50:42

10. 2011-11-7 17:50:43

11. 2011-11-7 17:50:44

12. 2011-11-7 17:50:45

13. 2011-11-7 17:50:46

14. 2011-11-7 17:50:47

15. 2011-11-7 17:50:48

16. 2011-11-7 17:50:49

17. 2011-11-7 17:50:50