READV(3)                   POSIX Programmer's Manual                  READV(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       readv -- read a vector

SSYYNNOOPPSSIISS
       #include <sys/uio.h>

       ssize_t readv(int _f_i_l_d_e_s, const struct iovec *_i_o_v, int _i_o_v_c_n_t);

DDEESSCCRRIIPPTTIIOONN
       The _r_e_a_d_v() function shall be equivalent to _r_e_a_d(), except as described
       below. The _r_e_a_d_v() function shall place the input data into the _i_o_v_c_n_t
       buffers specified by the members of the _i_o_v array: _i_o_v[0], _i_o_v[1], ...,
       _i_o_v[_i_o_v_c_n_t-1].  The _i_o_v_c_n_t argument is valid if greater than 0 and less
       than or equal to {IOV_MAX}.

       Each _i_o_v_e_c entry specifies the base address and length of an area in
       memory where data should be placed. The _r_e_a_d_v() function shall always
       fill an area completely before proceeding to the next.

       Upon successful completion, _r_e_a_d_v() shall mark for update the last data
       access timestamp of the file.

RREETTUURRNN VVAALLUUEE
       Refer to _r_e_a_d().

EERRRROORRSS
       Refer to _r_e_a_d().

       In addition, the _r_e_a_d_v() function shall fail if:

       EEIINNVVAALL The sum of the _i_o_v___l_e_n values in the _i_o_v array overflowed an
              ssssiizzee__tt.

       The _r_e_a_d_v() function may fail if:

       EEIINNVVAALL The _i_o_v_c_n_t argument was less than or equal to 0, or greater than
              {IOV_MAX}.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
   RReeaaddiinngg DDaattaa iinnttoo aann AArrrraayy
       The following example reads data from the file associated with the file
       descriptor _f_d into the buffers specified by members of the _i_o_v array.


           #include <sys/types.h>
           #include <sys/uio.h>
           #include <unistd.h>
           ...
           ssize_t bytes_read;
           int fd;
           char buf0[20];
           char buf1[30];
           char buf2[40];
           int iovcnt;
           struct iovec iov[3];

           iov[0].iov_base = buf0;
           iov[0].iov_len = sizeof(buf0);
           iov[1].iov_base = buf1;
           iov[1].iov_len = sizeof(buf1);
           iov[2].iov_base = buf2;
           iov[2].iov_len = sizeof(buf2);
           ...
           iovcnt = sizeof(iov) / sizeof(struct iovec);

           bytes_read = readv(fd, iov, iovcnt);
           ...

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       None.

RRAATTIIOONNAALLEE
       Refer to _r_e_a_d().

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _r_e_a_d(), _w_r_i_t_e_v()

       The Base Definitions volume of POSIX.1-2017, <<ssyyss__uuiioo..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                             READV(3)
