fileno() -- STDIO Function (libc)

Get file descriptor
#include <stdio.h>
int fileno(fp) FILE *fp;

fileno() returns  the file descriptor  associated with the  file stream fp.
The  file descriptor  is  the integer  returned  by open()  or creat();  it
corresponds to a FILE structure, as returned by the STDIO function fopen().

Example

This example reads a file descriptor and prints it on the screen.

#include <stdio.h>

main(argc,argv)
int argc; char *argv[];
{
    FILE *fp;
    int fd;

    if (argc !=2) {
        printf("Usage: fd_from_fp filename\n");
        exit(0);
    }

    if ((fp = fopen(argv[1], "r")) == NULL) {
        printf("Cannot open input file\n");
        exit(0);
    }

    fd = fileno(fp);
    printf("The file descriptor for %s is %d\n",
        argv[1], fd);
}

See Also

FILE,
file descriptor,
libc
POSIX Standard, §8.2.1

© 2012 by Stephen A. Ness