NAME
close
—
delete a descriptor
LIBRARY
library “libc”
SYNOPSIS
#include
<unistd.h>
int
close
(int
d);
DESCRIPTION
Theclose
()
system call deletes a descriptor from the per-process object reference table.
If this is the last reference to the underlying object, the object will be
deactivated. For example, on the last close of a file the current
seek pointer
associated with the file is lost; on the last close of a
socket(2) associated naming information and queued data are discarded;
on the last close of a file holding an advisory lock the lock is released (see
flock(2)).
When a process exits, all associated descriptors are
freed, but since there is a limit on active descriptors per processes, the
close
()
system call is useful when a large quantity of file descriptors are being
handled.
When a process calls
fork(2), all descriptors for the new child process reference the same
objects as they did in the parent before the
fork
(). If a
new process is then to be run using
execve(2), the process would normally inherit these descriptors. Most
of the descriptors can be rearranged with
dup2(2) or deleted with close
() before the
execve
() is attempted, but if some of these
descriptors will still be needed if the execve
()
fails, it is necessary to arrange for them to be closed only if the
execve
() succeeds. For this reason, the system
call
fcntl
(d, F_SETFD, 1);
is provided, which arranges that a descriptor
“d” will be closed after a successful
execve
();
the system call
fcntl
(d, F_SETFD, 0);
restores the default, which is to not close descriptor “d”.
RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.
ERRORS
close
() will fail if:
- [
EBADF
] - d is not an active descriptor.
- [
EINTR
] - An interrupt was received.
SEE ALSO
accept(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2)
STANDARDS
The close
() function conforms to
IEEE Std 1003.1-1990 (“POSIX.1”).
HISTORY
The close
() function appeared in
Version 1 AT&T UNIX.