1READV(3P) POSIX Programmer's Manual READV(3P)
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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.
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13 readv — read a vector
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16 #include <sys/uio.h>
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18 ssize_t readv(int fildes, const struct iovec *iov, int iovcnt);
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21 The readv() function shall be equivalent to read(), except as described
22 below. The readv() function shall place the input data into the iovcnt
23 buffers specified by the members of the iov array: iov[0], iov[1], ...,
24 iov[iovcnt−1]. The iovcnt argument is valid if greater than 0 and less
25 than or equal to {IOV_MAX}.
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27 Each iovec entry specifies the base address and length of an area in
28 memory where data should be placed. The readv() function shall always
29 fill an area completely before proceeding to the next.
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31 Upon successful completion, readv() shall mark for update the last data
32 access timestamp of the file.
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35 Refer to read().
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38 Refer to read().
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40 In addition, the readv() function shall fail if:
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42 EINVAL The sum of the iov_len values in the iov array overflowed an
43 ssize_t.
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45 The readv() function may fail if:
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47 EINVAL The iovcnt argument was less than or equal to 0, or greater than
48 {IOV_MAX}.
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50 The following sections are informative.
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53 Reading Data into an Array
54 The following example reads data from the file associated with the file
55 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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82 None.
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85 Refer to read().
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88 None.
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91 read(), writev()
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93 The Base Definitions volume of POSIX.1‐2008, <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, 2013 Edition, Standard for Information Technology
98 -- Portable Operating System Interface (POSIX), The Open Group Base
99 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
100 cal and Electronics Engineers, Inc and The Open Group. (This is
101 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
102 event of any discrepancy between this version and the original IEEE and
103 The Open Group Standard, the original IEEE and The Open Group Standard
104 is the referee document. The original Standard can be obtained online
105 at http://www.unix.org/online.html .
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107 Any typographical or formatting errors that appear in this page are
108 most likely to have been introduced during the conversion of the source
109 files to man page format. To report such errors, see https://www.ker‐
110 nel.org/doc/man-pages/reporting_bugs.html .
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114IEEE/The Open Group 2013 READV(3P)