Question

I need help using this given program and making it not create a hole in the file. Once compiled and executed this program creates a file that is 16394 bytes but has a hole in it. I need to make a file WITHOUT A HOLE that is the same size (16394 bytes) from this program. I know I need to remove/change the lseek portion. I just dont know what to replace it with. A write function?

Given Program:

#include "apue.h"
#include <fcntl.h>

char    buf1[] = "abcdefghij";
char    buf2[] = "ABCDEFGHIJ";

int
main(void)
{
        int             fd;

        if ((fd = creat("file.hole", FILE_MODE)) < 0)
                printf("creat error");

        if (write(fd, buf1, 10) != 10)
                printf("buf1 write error");
        /* offset now = 10 */

        if (lseek(fd, 16384, SEEK_SET) == -1)
                printf("lseek error");
        /* offset now = 16384 */

        if (write(fd, buf2, 10) != 10)
                printf("buf2 write error");
        /* offset now = 16394 */

        exit(0);
}

Answer 1

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>

char buf1[] = "abcdefghij";
char buf2[] = "ABCDEFGHIJ";

intmain(void)
{
        int fd;
        if ((fd = create("file.hole", FILE_MODE)) < 0)
                printf("creat error");

        if (write(fd, buf1, 10) != 10)
                printf("buf1 write error");
        /* offset now = 10 */

        if (lseek(fd, 16383, SEEK_SET) == -1)
                printf("lseek error");
        /* offset now = 16383 */
        

       /* write just one byte at the end, here its null char */
       result = write(fd, "", 1);
       if (result < 0) {
                close(fd);
                perror("Error writing a byte at the end of the file");
            return 1;
       }
       /* offset now = 16384 */

        if (write(fd, buf2, 10) != 10)
                printf("buf2 write error");
        /* offset now = 16394 */
        

        close(fd);
        exit(0);
}

--End of code--

Adding at least one byte of data (here I used NULL character), in the end, so that the hole doesn't get created in the file. The 'lseek' has been changed to 16383 and a NULL char '\0' has been written to pos 16384. Then buf2[] has been written next. OS will fill the next bytes (from 10 to 16383) with all zeroes, that will hopefully remove the whole. The file size also did not increase.

Please leave a "Thumbs Up", it will be of great help. Thanks.

Happy Studying.