READ(2)                 COMMAND REFERENCE                 READ(2)



NAME
     read, readv - read input

SYNOPSIS
     cc = read(fd, buf, nbytes)
     int cc, fd;
     char *buf;
     int nbytes;

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

     cc = readv(fd, iov, iovcnt)
     int cc, fd;
     struct iovec *iov;
     int iovcnt;

DESCRIPTION
     The read command attempts to read nbytes of data from the
     object referenced by the descriptor fd into the buffer
     pointed to by buf; readv performs the same action, but
     scatters the input data into iovcnt buffers specified by the
     members of the iovec array: iov[0], iov[1], ...,
     iov[iovcnt-1].

     The readv command is not supported for raw devices (e.g. raw
     disks, terminals).

     Commands read and readv return in cc the number of bytes
     read.

     For readv, the iovec structure is defined in <sys/uio.h> as:

          struct iovec {
               caddr_t   iov_base;
               int       iov_len;
          };

     Each iovec entry specifies the base address and length of an
     area in memory where data should be placed; readv always
     fills an area completely before proceeding to the next area.

     On objects capable of seeking, the read starts at a position
     given by the pointer associated with fd, 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.





Printed 4/6/89                                                  1

READ(2)                 COMMAND REFERENCE                 READ(2)



     Upon successful completion, read and readv return the number
     of bytes read and number of bytes placed in the buffer.  The
     system guarantees to read the number of bytes requested if
     the descriptor references a file which has that many bytes
     left before the end-of-file, but in no other cases.

     If cc = 0, then end-of-file has been reached.

DIAGNOSTICS
     Commands read and readv fail if one or more of the following
     are true:

     [EBADF]      Fd is not a valid file descriptor open for
                  reading.

     [EFAULT]     Buf points outside the allocated address space.

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

     [ENOBUFS]    Fd is a socket, and the system lacks sufficient
                  buffer space to do the read.

     [ENOTCONN]   Fd is a socket which is not connected.

     [EWOULDBLOCK]
                  Fd is in non-blocking mode, and doing the read
                  would cause a process to block.

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

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

     [EINVAL]     One of the iov_len values in the iov array is
                  negative.

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

     [ENXIO]      A readv command was attempted on an unsupported
                  raw device.

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

SEE ALSO
     dup(2), lseek(2), open(2), pipe(2), socket(2), and
     socketpair(2).



Printed 4/6/89                                                  2

%%index%%
na:240,76;
sy:316,1799;
de:2115,1881;4308,464;
di:4772,1667;
rv:6439,300;
se:6739,231;
%%index%%000000000120