Sams Teach Yourself C in 21 Days

Using Disk Files 461

16

LISTING16.6 fseek.c. Random file access with fseek()

1: /* Random access with fseek(). */

2:

3: #include <stdlib.h>

4: #include <stdio.h>

5:

6: #define MAX 50

7:

8: int main( void )

9: {

10: FILE *fp;

11: int data, count, array[MAX];

12: long offset;

13:

14: /* Initialize the array. */

15:

16: for (count = 0; count < MAX; count++)

17: array[count] = count * 10;

18:

19: /* Open a binary file for writing. */

20:

21: if ( (fp = fopen(“RANDOM.DAT”, “wb”)) == NULL)

22: {

23: fprintf(stderr, “\nError opening file.”);

24: exit(1);

25: }

26:

27: /* Write the array to the file, then close it. */

28:

29: if ( (fwrite(array, sizeof(int), MAX, fp)) != MAX)

30: {

31: fprintf(stderr, “\nError writing data to file.”);

32: exit(1);

33: }

34:

35: fclose(fp);

36:

37: /* Open the file for reading. */

38:

39: if ( (fp = fopen(“RANDOM.DAT”, “rb”)) == NULL)

40: {

41: fprintf(stderr, “\nError opening file.”);

42: exit(1);

43: }

44:

45: /* Ask user which element to read. Input the element */

46: /* and display it, quitting when -1 is entered. */

47:

48: while (1)

INPUT

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