O_ACCMODE

O_ACCMODE <0003>: When reading and writing files, it is used to retrieve the low 2-bit flag

O_RDONLY <00>: Read-only

O_WRONLY <01>: Write-only open

O_RDWR <02>: read/write enabled

The following program can be well understood:

1 # include <sys/types. h>

2 # include <fcntl. h>

3 # include "ourhdr. h"

4

5 int

6 main (int argc, char * argv [])

7 {

8 int accmode, val;

9 if (argc! = 2)

10 err_quit ("usage: a. out <descriptor #> ");

11

12 if (val = fcntl (atoi (argv [1]), F_GETFL, 0) <0)

13 err_sys ("fcntl error for fd % d", atoi (argv [1]);

14

15 accmode = val & O_ACCMODE;

16 if (accmode = O_RDONLY) printf ("read only ");

17 else if (accmode = O_WRONLY) printf ("write only ");

18 else if (accmode = O_RDWR) printf ("read write ");

19 else err_dump ("unknown access mode ");

20

21 if (val & O_APPEND) printf (", append ");

22 if (val & O_NONBLOCK) printf (", nonblocking ");

23 # if! Defined (_ POSIX_SOURCE) & defined (O_SYNC)

If (val & O_SYNC) printf (", synchronous writes ");

25 # endif

26 putchar ('\ n ');

27 exit (0 );

28}

The above code is selected from Unix Advanced environment programming.

O_ACCMODE