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readv(2) - readv, writev, readv, writev - read or write data into multiple buffers - man 2 readv

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



NAME
       readv, writev - read(2,n,1 builtins) or write(1,2) 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(1,n) associated with
       the file(1,n) descriptor fd into the multiple buffers described by vector.

       The writev() function writes at most count blocks described  by  vector
       to the file(1,n) associated with the file(1,n) descriptor fd.

       The pointer vector points to a struct iovec defined in(1,8) <sys/uio.h> as

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

       Buffers are processed in(1,8) the order specified.

       The  readv()  function  works  just  like  read(2,n,1 builtins)(2) except that multiple
       buffers are filled.

       The writev() function works just like  write(1,2)(2)  except  that  multiple
       buffers are written out.


RETURN VALUE
       On  success, the readv() function returns the number of bytes read(2,n,1 builtins); the
       writev() function returns the number of bytes written.  On error(8,n), -1 is
       returned, and errno is set(7,n,1 builtins) appropriately.

ERRORS
       The  errors  are  as  given for read(2,n,1 builtins)(2) and write(1,2)(2).  Additionally the
       following error(8,n) is defined.

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

CONFORMING TO
       4.4BSD  (the  readv  and  writev  functions first appeared in(1,8) 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(1,n) descriptors, with the functions  from  the  stdio
       library;  the results will be undefined and probably not what you want.

SEE ALSO
       read(2,n,1 builtins)(2), write(1,2)(2)



                                  2002-10-17                          READV(2)

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