1READV(3P)                  POSIX Programmer's Manual                 READV(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
10

NAME

12       readv — read a vector
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SYNOPSIS

15       #include <sys/uio.h>
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17       ssize_t readv(int fildes, const struct iovec *iov, int iovcnt);
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DESCRIPTION

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

34       Refer to read().
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ERRORS

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

52   Reading Data into an Array
53       The following example reads data from the file associated with the file
54       descriptor fd into the buffers specified by members of the iov array.
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57           #include <sys/types.h>
58           #include <sys/uio.h>
59           #include <unistd.h>
60           ...
61           ssize_t bytes_read;
62           int fd;
63           char buf0[20];
64           char buf1[30];
65           char buf2[40];
66           int iovcnt;
67           struct iovec iov[3];
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69           iov[0].iov_base = buf0;
70           iov[0].iov_len = sizeof(buf0);
71           iov[1].iov_base = buf1;
72           iov[1].iov_len = sizeof(buf1);
73           iov[2].iov_base = buf2;
74           iov[2].iov_len = sizeof(buf2);
75           ...
76           iovcnt = sizeof(iov) / sizeof(struct iovec);
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78           bytes_read = readv(fd, iov, iovcnt);
79           ...
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APPLICATION USAGE

82       None.
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RATIONALE

85       Refer to read().
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FUTURE DIRECTIONS

88       None.
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SEE ALSO

91       read(), writev()
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93       The Base Definitions volume of POSIX.1‐2017, <sys_uio.h>
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96       Portions of this text are reprinted and reproduced in  electronic  form
97       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
98       table Operating System Interface (POSIX), The Open Group Base  Specifi‐
99       cations  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of
100       Electrical and Electronics Engineers, Inc and The Open Group.   In  the
101       event of any discrepancy between this version and the original IEEE and
102       The Open Group Standard, the original IEEE and The Open Group  Standard
103       is  the  referee document. The original Standard can be obtained online
104       at http://www.opengroup.org/unix/online.html .
105
106       Any typographical or formatting errors that appear  in  this  page  are
107       most likely to have been introduced during the conversion of the source
108       files to man page format. To report such errors,  see  https://www.ker‐
109       nel.org/doc/man-pages/reporting_bugs.html .
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113IEEE/The Open Group                  2017                            READV(3P)
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