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close(2) [osx man page]

CLOSE(2)						      BSD System Calls Manual							  CLOSE(2)

NAME
close -- delete a descriptor SYNOPSIS
#include <unistd.h> int close(int fildes); DESCRIPTION
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. RETURN VALUES
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. ERRORS
The close() system call will fail if: [EBADF] fildes is not a valid, active file descriptor. [EINTR] Its execution was interrupted by a signal. [EIO] A previously-uncommitted write(2) encountered an input/output error. SEE ALSO
accept(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2) STANDARDS
Close() conforms to IEEE Std 1003.1-1988 (``POSIX.1''). 4th Berkeley Distribution April 19, 1994 4th Berkeley Distribution

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DUP(2)							      BSD System Calls Manual							    DUP(2)

NAME
dup, dup2 -- duplicate an existing file descriptor SYNOPSIS
#include <unistd.h> int dup(int fildes); int dup2(int fildes, int fildes2); DESCRIPTION
dup() duplicates an existing object descriptor and returns its value to the calling process (fildes2 = dup(fildes)). The argument fildes is a small non-negative integer index in the per-process descriptor table. The value must be less than the size of the table, which is returned by getdtablesize(2). The new descriptor returned by the call is the lowest numbered descriptor currently not in use by the process. The object referenced by the descriptor does not distinguish between fildes and fildes2 in any way. Thus if fildes2 and fildes are duplicate references to an open file, read(2), write(2) and lseek(2) calls all move a single pointer into the file, and append mode, non-blocking I/O and asynchronous I/O options are shared between the references. If a separate pointer into the file is desired, a different object reference to the file must be obtained by issuing an additional open(2) call. The close-on-exec flag on the new file descriptor is unset. In dup2(), the value of the new descriptor fildes2 is specified. If fildes and fildes2 are equal, then dup2() just returns fildes2; no other changes are made to the existing descriptor. Otherwise, if descriptor fildes2 is already in use, it is first deallocated as if a close(2) call had been done first. RETURN VALUES
Upon successful completion, the new file descriptor is returned. Otherwise, a value of -1 is returned and the global integer variable errno is set to indicate the error. ERRORS
The dup() and dup2() system calls will fail if: [EBADF] fildes is not an active, valid file descriptor. [EINTR] Execution is interrupted by a signal. [EMFILE] Too many file descriptors are active. The dup2() system call will fail if: [EBADF] fildes2 is negative or greater than the maximum allowable number (see getdtablesize(2)). SEE ALSO
accept(2), close(2), fcntl(2), getdtablesize(2), open(2), pipe(2), socket(2), socketpair(2) STANDARDS
dup() and dup2() are expected to conform to IEEE Std 1003.1-1988 (``POSIX.1''). 4th Berkeley Distribution December 1, 2010 4th Berkeley Distribution

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