readv(3p) — Linux manual page

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

PROLOG

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

NAME

       readv — read a vector

SYNOPSIS

       #include <sys/uio.h>

       ssize_t readv(int fildes, const struct iovec *iov, int iovcnt);

DESCRIPTION

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

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

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

RETURN VALUE

       Refer to read(3p).

ERRORS

       Refer to read(3p).

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

       EINVAL The sum of the iov_len values in the iov array overflowed
              an ssize_t.

       The readv() function may fail if:

       EINVAL The iovcnt argument was less than or equal to 0, or
              greater than {IOV_MAX}.

       The following sections are informative.

EXAMPLES

   Reading Data into an Array
       The following example reads data from the file associated with
       the file descriptor fd into the buffers specified by members of
       the iov 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);
           ...

APPLICATION USAGE

       None.

RATIONALE

       Refer to read(3p).

FUTURE DIRECTIONS

       None.

SEE ALSO

       read(3p), writev(3p)

       The Base Definitions volume of POSIX.1‐2017, sys_uio.h(0p)

COPYRIGHT

       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(3P)

Pages that refer to this page: sys_uio.h(0p), read(3p), writev(3p)

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