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ferror.3: Warn about closing the result of fileno() 

Since adding checking to Android's bionic for file descriptor
double-closes, we've found that the most common cause of these
bugs is incorrect use of fileno(3). There appears to be a common
misconception that it transfers ownership of the file descriptor
to the caller.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Elliot Hughes 2018-10-01 10:33:21 -07:00 committed by Michael Kerrisk
parent b79b66d119
commit c36a6bedf6
1 changed files with 9 additions and 1 deletions
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10
man3/ferror.3
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@ -89,7 +89,15 @@ The function
.BR fileno ()
examines the argument
.I stream
and returns its integer file descriptor.
and returns the integer file descriptor used to implement this stream.
The file descriptor is still owned by
.I stream
and will be closed when
.BR fclose (3)
is called.
Duplicate the file descriptor with
.BR dup (2)
before passing it to code that might close it.
.PP
For nonlocking counterparts, see
.BR unlocked_stdio (3).