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writev(3p) — Linux manual page

WRITEV(3P)              POSIX Programmer's ManualWRITEV(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

       writev — write a vector

SYNOPSIS        top

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

DESCRIPTION        top

       Thewritev() function shall be equivalent towrite(), except as       described below. Thewritev() function shall gather output data       from 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}, as defined       in<limits.h>.       Eachiovec entry specifies the base address and length of an area       in memory from which data should be written. Thewritev() function       shall always write a complete area before proceeding to the next.       Iffildes refers to a regular file and all of theiov_len members       in the array pointed to byiov are 0,writev() shall return 0 and       have no other effect. For other file types, the behavior is       unspecified.       If the sum of theiov_len values is greater than {SSIZE_MAX}, the       operation shall fail and no data shall be transferred.

RETURN VALUE        top

       Upon successful completion,writev() shall return the number of       bytes actually written. Otherwise, it shall return a value of -1,       the file-pointer shall remain unchanged, anderrno shall be set to       indicate an error.

ERRORS        top

       Refer towrite(3p).       In addition, thewritev() function shall fail if:EINVALThe sum of theiov_len values in theiov array would              overflow anssize_t.       Thewritev() function may fail and seterrno to:EINVALTheiovcnt argument was less than or equal to 0, or greater              than {IOV_MAX}.The following sections are informative.

EXAMPLES        top

Writing Data from an Array       The following example writes data from the buffers specified by       members of theiov array to the file associated with the file       descriptorfd.           #include <sys/types.h>           #include <sys/uio.h>           #include <unistd.h>           ...           ssize_t bytes_written;           int fd;           char *buf0 = "short string\n";           char *buf1 = "This is a longer string\n";           char *buf2 = "This is the longest string in this example\n";           int iovcnt;           struct iovec iov[3];           iov[0].iov_base = buf0;           iov[0].iov_len = strlen(buf0);           iov[1].iov_base = buf1;           iov[1].iov_len = strlen(buf1);           iov[2].iov_base = buf2;           iov[2].iov_len = strlen(buf2);           ...           iovcnt = sizeof(iov) / sizeof(struct iovec);           bytes_written = writev(fd, iov, iovcnt);           ...

APPLICATION USAGE        top

       None.

RATIONALE        top

       Refer towrite(3p).

FUTURE DIRECTIONS        top

       None.

SEE ALSO        top

readv(3p),write(3p)       The Base Definitions volume of POSIX.1‐2017,limits.h(0p),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                2017WRITEV(3P)

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

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