setting the default file permissoins

rajesh_b · 09-23-2004, 02:08 AM

I am trying to copy files from one folder to another folder. i am doing this using the functions open,read,write. what is the problem is that the file permissions are changed. how can i ensure that the file must have the same permissions as the original file. for example if the source file has permissions 644 then the copied file in the other folder must have the same permissios. I know that chmod function can be used to change the permission. But how can i know the permission of original file.

Thanx in advance,
rajesh

itsme86 · 09-23-2004, 02:11 AM

Check out 'man stat'. Particularly, the st_mode member of struct stat.

rajesh_b · 09-23-2004, 02:19 AM

Thanx for u r immediate reply. Finally i got the solution.
I am changing the file permission of the newfile with the statement
chmod(filename,p_stat->st_mode&0777);

thanx a lot.

itsme86 · 09-23-2004, 02:36 AM

This is another way to do it:

Code:

itsme@dreams:~/C$ cat mycp.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char **argv)
{
  int fdin, fdout;
  struct stat st;
  char buf[BUFSIZ];
  int n_read;

  if(argc != 3)
  {
    puts("Usage: mycp <source> <destination>");
    exit(1);
  }
  if((fdin = open(argv[1], O_RDONLY)) == -1)
  {
    printf("open(): %s\n", strerror(errno));
    exit(1);
  }
  if(fstat(fdin, &st) == -1)
  {
    printf("stat(): %s\n", strerror(errno));
    exit(1);
  }

  umask(0);
  if((fdout = open(argv[2], O_WRONLY|O_CREAT|O_TRUNC, st.st_mode)) == -1)
  {
    printf("open(): %s\n", strerror(errno));
    exit(1);
  }

  while((n_read = read(fdin, buf, sizeof(buf))) > 0)
  {
    if(write(fdout, buf, n_read) == -1)
    {
      printf("write(): %s\n", strerror(errno));
      exit(1);
    }
  }

  close(fdin);
  close(fdout);

  if(n_read == -1)
  {
    printf("read(): %s\n", strerror(errno));
    exit(1);
  }

  return 0;
}

Example:

Code:

itsme@dreams:~/C$ head -c 50000 /dev/urandom > file1.garbage
itsme@dreams:~/C$ ls -l file1.garbage
-rw-r--r--    1 itsme    users       50000 Sep 23 00:34 file1.garbage
itsme@dreams:~/C$ ./mycp file1.garbage file2.garbage
itsme@dreams:~/C$ ls -l file2.garbage
-rw-r--r--    1 itsme    users       50000 Sep 23 00:34 file2.garbage
itsme@dreams:~/C$ chmod a+w file2.garbage
itsme@dreams:~/C$ ls -l file2.garbage
-rw-rw-rw-    1 itsme    users       50000 Sep 23 00:34 file2.garbage
itsme@dreams:~/C$ ./mycp file2.garbage file3.garbage
itsme@dreams:~/C$ ls -l file3.garbage
-rw-rw-rw-    1 itsme    users       50000 Sep 23 00:35 file3.garbage
itsme@dreams:~/C$