HP 3000 Manuals HP 3000 Manuals
dup
Duplicates an open file descriptor.
Syntax
#include <fcntl.h>
int dup (int fildes);
Parameters
fildes A file descriptor.
Return Values
n A non-negative integer representing the new file
descriptor.
-1 An error occurred and errno is set to one of the following
values:
EBADF The fildes parameter is not a valid open file
descriptor.
EMFILE The maximum number of file descriptors are
currently open.
Description
The dup function returns the lowest-numbered available file descriptor.
The new file descriptor returned by dup() refers to the same open file
description as fildes. The data in the file is not duplicated; only the
file descriptor is duplicated.
Using dup() to create two file descriptors that point to the same file is
different from opening the file twice with open(). With dup(), both file
descriptors use the same file table entry, and the same file offset is
used for reads and writes. With open(), multiple file descriptors and
file table entries are created, and multiple file offset variables are
used with reads and writes.
The new file descriptor has the following in common with the original
file descriptor:
* Both share the same open file description.
* Both share the same file position indicator.
* Both share the same access mode.
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NOTE If linking with the POSIX/iX library, refer to the description of
dup() located in the MPE/iX Developer's Kit Reference Manual.
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See Also
open()