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#include <unistd.h> int pipe(int fildes[2]); int pipe2(int fildes[2], int flags);
The pipe() and pipe2() functions create an I/O mechanism called a pipe and returns two file descriptors, fildes[0] and fildes[1]. The files associated with fildes[0] and fildes[1] are streams and are both opened for reading and writing. The pipe() call will clear the O_NDELAY, O_NONBLOCK, and FD_CLOEXEC flags on both file descriptors. The fcntl(2) function can be used to set these flags.
The pipe2() call will clear the O_NDELAY on both filedescriptors. The flags argument may be used to specify attributes on both file descriptors. pipe2() called with a flags value of 0 will behave identically to pipe(). Values for flags are constructed by a bitwise-inclusive-OR of flags from the following list, defined in <fcntl.h>. O_NONBLOCK
Both file descriptors will be placed in non-blocking mode. This corresponds to the O_NONBLOCK flag to fcntl(2).
Both file descriptors will be opened with the FD_CLOEXEC flag set. Both file descriptors will be closed prior to any future exec() calls.
A read from fildes[0] accesses the data written to fildes[1] on a first-in-first-out (FIFO) basis and a read from fildes[1] accesses the data written to fildes[0] also on a FIFO basis.
Upon successful completion pipe() marks for update the st_atime, st_ctime, and st_mtime fields of the pipe.
Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.
The pipe() and pipe2() functions will fail if: EMFILE
More than {OPEN_MAX} file descriptors are already in use by this process.
The number of simultaneously open files in the system would exceed a system-imposed limit.
The fildes[2] argument points to an illegal address.
The pipe2() function will also fail if: EINVAL
The flags argument is illegal. Valid flags are zero or a bitwise inclusive-OR of O_CLOEXEC and O_NONBLOCK.
See attributes(7) for descriptions of the following attributes:
| ATTRIBUTE TYPE ATTRIBUTE VALUE |
| Interface Stability Standard |
| MT-Level Async-Signal-Safe |
sh (1), fcntl (2), fstat (2), getmsg (2), open (2), poll (2), putmsg (2), read (2), write (2), streamio (4I), attributes (7), standards (7)
Since a pipe is bi-directional, there are two separate flows of data. Therefore, the size (st_size) returned by a call to fstat(2) with argument fildes[0] or fildes[1] is the number of bytes available for reading from fildes[0] or fildes[1] respectively. Previously, the size (st_size) returned by a call to fstat() with argument fildes[1] (the write-end) was the number of bytes available for reading from fildes[0] (the read-end).