4.3BSD-UWisc/man/cat2/read.2

READ(2)             UNIX Programmer's Manual              READ(2)



NAME
     read, readv - read input

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

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

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

DESCRIPTION
     _R_e_a_d attempts to read _n_b_y_t_e_s of data from the object refer-
     enced by the descriptor _d into the buffer pointed to by _b_u_f.
     _R_e_a_d_v performs the same action, but scatters the input data
     into the _i_o_v_c_n_t buffers specified by the members of the _i_o_v
     array: iov[0], iov[1], ..., iov[iovcnt-1].

     For _r_e_a_d_v, the _i_o_v_e_c structure is defined as

          struct iovec {
               caddr_t   iov_base;
               int  iov_len;
          };

     Each _i_o_v_e_c entry specifies the base address and length of an
     area in memory where data should be placed. _R_e_a_d_v will
     always fill an area completely before proceeding to the
     next.

     On objects capable of seeking, the _r_e_a_d starts at a position
     given by the pointer associated with _d (see _l_s_e_e_k(2)).  Upon
     return from _r_e_a_d, 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, _r_e_a_d and _r_e_a_d_v 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.





Printed 12/27/86          May 23, 1986                          1






READ(2)             UNIX Programmer's Manual              READ(2)



     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 vari-
     able _e_r_r_n_o is set to indicate the error.

ERRORS
     _R_e_a_d and _r_e_a_d_v 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]       _B_u_f 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, _r_e_a_d_v may return one of the following errors:

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

     [EINVAL]       One of the _i_o_v__l_e_n values in the _i_o_v array
                    was negative.

     [EINVAL]       The sum of the _i_o_v__l_e_n values in the _i_o_v
                    array overflowed a 32-bit integer.

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

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








Printed 12/27/86          May 23, 1986                          2