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pipe - Create an interprocess channel
int filedes );
Interfaces documented on this reference page conform to industry standards
pipe(): XSH4.0, XSH4.2, XSH5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
filedes Specifies the address of an array of two integers into which the
new file descriptors are placed.
The pipe() function creates a unidirectional interprocess channel called a
pipe, and returns two file descriptors, filedes and filedes. The file
descriptor specified by the filedes parameter is opened for reading and
the file descriptor specified by the filedes parameter is opened for
writing. Their integer values will be the two lowest available at the time
of the call to the pipe() function.
A process has the pipe open for reading if it has a file descriptor open
that refers to the read end, filedes. A process has the pipe open for
writing if it has a file descriptor open that refers to the write end,
filedes. A read operation on file descriptor filedes accesses the
data written to filedes on a first-in, first-out (FIFO) basis.
In the System V compatiblity environment, filedes and filedes
are STREAMS based and are bidirectional. Data written on filedes
appears on filedes and vice versa. Data is read in a first-in,
first-out (FIFO) basis.
The O_NONBLOCK and the FD_CLOEXC flags are set clear on both file
descriptors. (The fcntl() function can be used to set the O_NONBLOCK flag.)
Upon successful completion, the pipe() function marks the st_atime,
st_ctime and st_mtime fields of the pipe for update.
[Tru64 UNIX] When a read() or write() system call on a pipe is interrupted
by a signal and no bytes have been transferred through the pipe, the read()
or write() system call returns a -1 and errno is set to [EINTR]. This
behavior differs from behavior in early releases of the operating system,
when both system calls either restarted the transfer or caused errno to be
set to [EINTR], depending on the setting of the SA_RESTART flag for the
[Tru64 UNIX] As a result of this change, applications must now either
handle the [EINTR] return or block any expected signals for the duration of
the read or write operation.
[Tru64 UNIX] When compiled in the X/Open UNIX environment, calls to the
pipe() function are internally renamed by prepending _E to the function
name. When you are debugging a module that includes the pipe() function and
for which _XOPEN_SOURCE_EXTENDED has been defined, use _Epipe to refer to
the pipe() call. See standards(5) for further information.
Upon successful completion, a value of 0 (zero) is returned. If the pipe()
function fails, a value of -1 is returned and errno is set to indicate the
If the pipe() function fails, errno may be set to one of the following
[Tru64 UNIX] The filedes parameter is an invalid address.
[EINTR] [Tru64 UNIX] A read() or a write() call on a pipe is interrupted
by a signal and no bytes have been transferred through the pipe.
More than OPEN_MAX-2 file descriptors are already opened by this
[Tru64 UNIX] More than getdtablesize(2) file descriptors are
already opened by this process.
The system file table is full, or the device containing pipes has
no free i-nodes.
[Tru64 UNIX] The system was unable to allocate kernel memory for
more file descriptors.
Functions: fcntl(2), getmsg(2), getdtablesize(2), poll(2), putmsg(2),
read(2), select(2), write(2)
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