close - delete a descriptor
int close(int d)
The close call deletes a descriptor from the per-process object reference
table. If this is the last reference to the underlying object, then it
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 TCP/IP descriptor 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 fcntl(2)).
A close of all of a process's descriptors is automatic on exit, but since
there is a limit on the number of active descriptors per process, close
is necessary for programs that deal with many descriptors.
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, flags)''
is provided, that can be used to mark a descriptor "close on exec" by
setting the FD_CLOEXEC flag:
fcntl(d, F_SETFD, fcntl(d, F_GETFD) | FD_CLOEXEC);
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.
Close will fail if:
[EBADF] D is not an active descriptor.
open(2), pipe(2), execve(2), fcntl(2).