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READ(2)			    BSD	System Calls Manual		       READ(2)

     read, readv, pread	-- read	input

     Standard C	Library	(libc, -lc)

     #include <sys/types.h>
     #include <sys/uio.h>
     #include <unistd.h>

     read(int d, void *buf, size_t nbytes);

     readv(int d, const	struct iovec *iov, int iovcnt);

     pread(int d, void *buf, size_t nbytes, off_t offset);

     The read()	system call attempts to	read nbytes of data from the object
     referenced	by the descriptor d into the buffer pointed to by buf.	The
     readv() system call performs the same action, but scatters	the input data
     into the iovcnt buffers specified by the members of the iov array:
     iov[0], iov[1], ..., iov[iovcnt-1].  The pread() system call performs the
     same function, but	reads from the specified position in the file without
     modifying the file	pointer.

     For readv(), the iovec structure is defined as:

	   struct iovec	{
		   void	  *iov_base;  /* Base address. */
		   size_t iov_len;    /* Length. */

     Each iovec	entry specifies	the base address and length of an area in mem-
     ory where data should be placed.  The readv() system call will always
     fill an area completely before proceeding to the next.

     On	objects	capable	of seeking, the	read() starts at a position given by
     the pointer associated with d (see	lseek(2)).  Upon return	from read(),
     the pointer is incremented	by the number of bytes actually	read.

     Objects that are not capable of seeking always read from the current po-
     sition.  The value	of the pointer associated with such an object is unde-

     Upon successful completion, read(), readv(), and pread() return the num-
     ber of bytes actually read	and placed in the buffer.  The system guaran-
     tees to read the number of	bytes requested	if the descriptor references a
     normal file that has that many bytes left before the end-of-file, but in
     no	other case.

     If	successful, the	number of bytes	actually read is returned.  Upon read-
     ing end-of-file, zero is returned.	 Otherwise, a -1 is returned and the
     global variable errno is set to indicate the error.

     The read(), readv(), and pread() system calls will	succeed	unless:

     [EBADF]		The d argument is not a	valid file or socket descrip-
			tor open for reading.

     [EFAULT]		The buf	argument points	outside	the allocated address

     [EIO]		An I/O error occurred while reading from the file sys-

     [EINTR]		A read from a slow device was interrupted before any
			data arrived by	the delivery of	a signal.

     [EINVAL]		The pointer associated with d was negative.

     [EAGAIN]		The file was marked for	non-blocking I/O, and no data
			were ready to be read.

     [EISDIR]		The file descriptor is associated with a directory re-
			siding on a filesystem that does not allow regular
			read operations	on directories (e.g. NFS).

     [EOPNOTSUPP]	The file descriptor is associated with a filesystem
			and file type that do not allow	regular	read opera-
			tions on it.

     In	addition, readv() may return one of the	following errors:

     [EINVAL]		The iovcnt argument was	less than or equal to 0, or
			greater	than 16.

     [EINVAL]		One of the iov_len values in the iov array was nega-

     [EINVAL]		The sum	of the iov_len values in the iov array over-
			flowed a 32-bit	integer.

     [EFAULT]		Part of	the iov	points outside the process's allocated
			address	space.

     The pread() system	call may also return the following errors:

     [EINVAL]		The specified file offset is invalid.

     [ESPIPE]		The file descriptor is associated with a pipe, socket,
			or FIFO.

     dup(2), fcntl(2), getdirentries(2), open(2), pipe(2), select(2),
     socket(2),	socketpair(2), fread(3), readdir(3)

     The read()	system call is expected	to conform to ISO/IEC 9945-1:1990
     ("POSIX.1").  The readv() and pread() system calls	are expected to	con-
     form to X/Open Portability	Guide Issue 4, Version 2 ("XPG4.2").

     The pread() function appeared in AT&T System V Release 4 UNIX.  The
     readv() system call appeared in 4.2BSD.  The read() function appeared in
     Version 6 AT&T UNIX.

BSD			       February	26, 1994			   BSD


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