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readv(3p) — Linux manual page

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

PROLOG        top

       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        top

       readv — read a vector

SYNOPSIS        top

       #include <sys/uio.h>       ssize_t readv(intfildes, const struct iovec *iov, intiovcnt);

DESCRIPTION        top

       Thereadv() function shall be equivalent toread(), except as       described below. Thereadv() function shall place the input data       into theiovcnt buffers specified by the members of theiov array:iov[0],iov[1], ...,iov[iovcnt-1].  Theiovcnt argument is valid       if greater than 0 and less than or equal to {IOV_MAX}.       Eachiovec entry specifies the base address and length of an area       in memory where data should be placed. Thereadv() 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        top

       Refer toread(3p).

ERRORS        top

       Refer toread(3p).       In addition, thereadv() function shall fail if:EINVALThe sum of theiov_len values in theiov array overflowed              anssize_t.       Thereadv() function may fail if:EINVALTheiovcnt argument was less than or equal to 0, or greater              than {IOV_MAX}.The following sections are informative.

EXAMPLES        top

Reading Data into an Array       The following example reads data from the file associated with the       file descriptorfd into the buffers specified by members of theiov 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        top

       None.

RATIONALE        top

       Refer toread(3p).

FUTURE DIRECTIONS        top

       None.

SEE ALSO        top

read(3p),writev(3p)       The Base Definitions volume of POSIX.1‐2017,sys_uio.h(0p)

COPYRIGHT        top

       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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017READV(3P)

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

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