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READ(2)			  FreeBSD System Calls Manual		       READ(2)

NAME
     read, readv -- read input

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

     ssize_t
     read(int d, char *buf, size_t nbytes);

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

DESCRIPTION
     Read() attempts to	read nbytes of data from the object referenced by the
     descriptor	d into the buffer pointed to by	buf.  Readv() performs the
     same action, but scatters the input data into the iovcnt buffers speci-
     fied by the members of the	iov array: iov[0], iov[1], ...,	iov[iovcnt-1].

     For readv(), the iovec structure is defined as
	   struct iovec	{
		   caddr_t iov_base;
		   int	   iov_len;
	   };

     Each iovec	entry specifies	the base address and length of an area in mem-
     ory where data should be placed.  Readv() will always fill	an area	com-
     pletely 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
     position.	The value of the pointer associated with such an object	is
     undefined.

     Upon successful completion, read()	and readv() return the number of bytes
     actually read and placed in the buffer.  The system guarantees 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.

RETURN VALUES
     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.

ERRORS
     Read() and	readv()	will succeed unless:

     [EBADF]		D is not a valid file or socket	descriptor open	for
			reading.

     [EFAULT]		Buf points outside the allocated address space.

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

     [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.

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

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

     [EINVAL]		Iovcnt was less	than or	equal to 0, or greater than
			16.

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

     [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.

SEE ALSO
     dup(2), fcntl(2), open(2),	pipe(2), select(2), socket(2), socketpair(2)

STANDARDS
     Read() is expected	to conform to IEEE Std 1003.1-1988 (``POSIX'').

HISTORY
     The readv() function call appeared	in 4.2BSD.  A read function call
     appeared in Version 6 AT&T	UNIX.

4th Berkeley Distribution	March 10, 1991	     4th Berkeley Distribution

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY

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