NAME
fileno — map a
stream pointer to a file descriptor
SYNOPSIS
int fileno(FILE *stream);
DESCRIPTION
The fileno () function shall return the
integer file descriptor associated with the stream pointed to by
stream.
RETURN VALUE
Upon successful completion, fileno ()
shall return the integer value of the file descriptor associated with
stream. Otherwise, the value -1 shall be returned and
errno
set to indicate the error.
ERRORS
The fileno () function may fail if:
- [EBADF]
- The stream argument is not a valid stream, or the stream is not associated with a file.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
Without some specification of which file descriptors are associated with these streams, it is impossible for an application to set up the streams for another application it starts with fork(3) and exec. In particular, it would not be possible to write a portable version of the sh(1) command interpreter (although there may be other constraints that would prevent that portability).
FUTURE DIRECTIONS
None.
SEE ALSO
V2_chap02(3) , dirfd(3) , fdopen(3) , fopen(3) , stdin(3)
XBD <stdio.h>
CHANGE HISTORY
First released in Issue 1. Derived from Issue 1 of the SVID.
Issue 6
The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:
- The [EBADF] optional error condition is added.
Issue 7
SD5-XBD-ERN-99 is applied, changing the definition of the [EBADF] error.