1READV(P)                   POSIX Programmer's Manual                  READV(P)
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NAME

6       readv - read a vector
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SYNOPSIS

9       #include <sys/uio.h>
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11       ssize_t readv(int fildes, const struct iovec *iov, int iovcnt);
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13

DESCRIPTION

15       The readv() function shall be equivalent to read(), except as described
16       below. The readv() function shall place the input data into the  iovcnt
17       buffers specified by the members of the iov array: iov[0], iov[1], ...,
18       iov[ iovcnt-1].  The iovcnt argument is valid if  greater  than  0  and
19       less than or equal to {IOV_MAX}.
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21       Each  iovec  entry  specifies the base address and length of an area in
22       memory where data should be placed. The readv() function  shall  always
23       fill an area completely before proceeding to the next.
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25       Upon  successful completion, readv() shall mark for update the st_atime
26       field of the file.
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RETURN VALUE

29       Refer to read() .
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ERRORS

32       Refer to read() .
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34       In addition, the readv() function shall fail if:
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36       EINVAL The sum of the iov_len values in the  iov  array  overflowed  an
37              ssize_t.
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40       The readv() function may fail if:
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42       EINVAL The iovcnt argument was less than or equal to 0, or greater than
43              {IOV_MAX}.
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45
46       The following sections are informative.
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EXAMPLES

49   Reading Data into an Array
50       The following example reads data from the file associated with the file
51       descriptor fd into the buffers specified by members of the iov array.
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53
54              #include <sys/types.h>
55              #include <sys/uio.h>
56              #include <unistd.h>
57              ...
58              ssize_t bytes_read;
59              int fd;
60              char buf0[20];
61              char buf1[30];
62              char buf2[40];
63              int iovcnt;
64              struct iovec iov[3];
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66
67              iov[0].iov_base = buf0;
68              iov[0].iov_len = sizeof(buf0);
69              iov[1].iov_base = buf1;
70              iov[1].iov_len = sizeof(buf1);
71              iov[2].iov_base = buf2;
72              iov[2].iov_len = sizeof(buf2);
73              ...
74              iovcnt = sizeof(iov) / sizeof(struct iovec);
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76
77              bytes_read = readv(fd, iov, iovcnt);
78              ...
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APPLICATION USAGE

81       None.
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RATIONALE

84       Refer to read() .
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FUTURE DIRECTIONS

87       None.
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SEE ALSO

90       read()    ,    writev()    ,    the    Base   Definitions   volume   of
91       IEEE Std 1003.1-2001, <sys/uio.h>
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94       Portions of this text are reprinted and reproduced in  electronic  form
95       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
96       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
97       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
98       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
99       event of any discrepancy between this version and the original IEEE and
100       The Open Group Standard, the original IEEE and The Open Group  Standard
101       is  the  referee document. The original Standard can be obtained online
102       at http://www.opengroup.org/unix/online.html .
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106IEEE/The Open Group                  2003                             READV(P)
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