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cfilefile-iostdio

Why is fileno failing to return a valid descriptor?

I'm opening a stream with funopen

FILE *fin = funopen(cookie, readfn, NULL, NULL, closefn);
if (fin == NULL)
{
    handle_error();
    return -1;
}
int fdin = fileno(fin);

The call to funopen succeeds but fileno(fin) returns -1.

How can I get the file descriptor? Thanks.

Solution

  • A FILE opened with funopen (which is not part of any standard, by the way; AFAIK it's a BSD extension) does not have an underlying file descriptor. It has the cookie instead. I don't know what you wanted the file descriptor for, but you're probably out of luck.