| CLOSE(2) | System Calls Manual | CLOSE(2) |
close — delete a
descriptor
#include
<unistd.h>
int
close(int fildes);
The
close()
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 further
flock(2)).
When a process exits, all associated file descriptors
are freed, but since there is a limit on active descriptors per processes,
the close()
function call is useful when a large quantity of file descriptors are being
handled.
When a process forks (see
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 if the execve succeeds. For this
reason, the call “fcntl(d, F_SETFD,
1)” is provided, which arranges that a descriptor will be
closed after a successful execve; the call “fcntl(d,
F_SETFD, 0)” restores the default, which is to not close the
descriptor.
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and the global integer variable errno is set to indicate the error.
The close() system call will fail if:
accept(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2)
close() conforms to IEEE
Std 1003.1-1988 (“POSIX.1”).
| April 19, 1994 | BSD 4 |