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().

ERRORS
Refer to read().

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().

FUTURE DIRECTIONS
None.

SEE ALSO
read(), writev()

The Base Definitions volume of POSIX.1-2017, <sys_uio.h>

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 .