readv

READV(2)		  Linux Programmer’s Manual		     READV(2)



NAME
       readv, writev - read or write data into multiple buffers

SYNOPSIS
       #include <sys/uio.h>

       ssize_t readv(int fd, const struct iovec *vector, int count);

       ssize_t writev(int fd, const struct iovec *vector, int count);

DESCRIPTION
       The  readv() function reads count blocks from the file associated with
       the file descriptor fd into the multiple buffers described by  vector.

       The  writev() function writes at most count blocks described by vector
       to the file associated with the file descriptor fd.

       The pointer vector points to a struct iovec defined in <sys/uio.h> as

	  struct iovec {
	      void *iov_base;	/* Starting address */
	      size_t iov_len;	/* Number of bytes */
	  };

       Buffers are processed in the order specified.

       The readv() function works just	like  read(2)  except  that  multiple
       buffers are filled.

       The  writev()  function	works just like write(2) except that multiple
       buffers are written out.


RETURN VALUE
       On success, the readv() function returns the number of bytes read; the
       writev()	 function  returns the number of bytes written.	 On error, -1
       is returned, and errno is set appropriately.

ERRORS
       The errors are as given for read(2) and	write(2).   Additionally  the
       following error is defined.

       EINVAL The  sum	of the iov_len values overflows an ssize_t value. Or,
	      the vector count count is less then zero or  greater  than  the
	      permitted maximum.

CONFORMING TO
       4.4BSD  (the  readv  and	 writev functions first appeared in BSD 4.2),
       Unix98, POSIX 1003.1-2001.  Linux libc5 used size_t as the type of the
       count parameter, and int as return type for these functions.

BUGS
       It  is  not  advisable  to  mix	calls  to  functions  like readv() or
       writev(), which operate on file descriptors, with the  functions	 from
       the stdio library; the results will be undefined and probably not what
       you want.

SEE ALSO
       read(2), write(2)



				  2002-10-17			     READV(2)