Write your own dup2 function that performs the same service as the dup2 function described in Section 3.12, without calling the fcntl function. Be sure to handle errors correctly.

An existing file descriptor is duplicated by either of the following functions:

#include <unistd.h>

int dup(int fd);

int dup2(int fd, int fd2);

Both return: new file descriptor if OK, −1 on error

The new file descriptor returned by dup is guaranteed to be the lowest-numbered

available file descriptor. With dup2, we specify the value of the new descriptor with the

fd2 argument. If fd2 is already open, it is first closed. If fd equals fd2, then dup2 returns

fd2 without closing it. Otherwise, the FD_CLOEXEC file descriptor flag is cleared for fd2,

so that fd2 is left open if the process calls exec.

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

#include    <stdio.h>

#include <unistd.h>

char arr[] = "my name is mydup\n";

int main()

{

    int fd1, fd2;

    char pidstr[128] = "\0";

    fd1 = open ("~/test/file_for_dup", O_CREAT|O_RDWR);

    if (fd1 < 0) {

        perror ("open");

        exit(-1);

    }

    sprintf (pidstr, "/proc/self/fd/%d", fd1);

    printf ("pidstr: %d %s\n", fd1, pidstr);

    write (fd1, arr, sizeof(arr));

    fd2 = open (pidstr, O_RDWR);

    if (fd2 < 0) {

        perror ("open");

        exit(-1);

    }

    lseek (fd2, sizeof (arr), SEEK_SET);

    write (fd2, arr, sizeof(arr));

    close (fd2);

    close (fd1);

}