READ(2) 							System Calls Manual							   READ(2)

NAME

       read, readv - read input

SYNOPSIS

       cc = read(d, buf, nbytes)
       int cc, d;
       char *buf;
       unsigned short nbytes;

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

       cc = readv(d, iov, iovcnt)
       int cc, 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  specified  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;
		   u_short   iov_len;
	      };

       Each  iovec  entry  specifies the base address and length of an area in memory where data should be placed.  Readv 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 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.

       If the returned value is 0, then end-of-file has been reached.

RETURN VALUE

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

ERRORS

       Read and readv will fail if one or more of the following are true:

       [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 system.

       [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]       The sum of the iov_len values in the iov array overflowed a short.

       [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)

4th Berkeley Distribution					  August 1, 1987							   READ(2)