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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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READV(3P) POSIX Programmer's Manual READV(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
readv — read a vector
#include <sys/uio.h>
ssize_t readv(int fildes, const struct iovec *iov, int iovcnt);
The readv() function shall be equivalent to read(), except as
described below. The readv() function shall place the input data
into the iovcnt buffers specified by the members of the iov array:
iov[0], iov[1], ..., iov[iovcnt-1]. The iovcnt argument is valid
if greater than 0 and less than or equal to {IOV_MAX}.
Each iovec entry specifies the base address and length of an area
in memory where data should be placed. The readv() function shall
always fill an area completely before proceeding to the next.
Upon successful completion, readv() shall mark for update the last
data access timestamp of the file.
Refer to read(3p).
Refer to read(3p).
In addition, the readv() function shall fail if:
EINVAL The sum of the iov_len values in the iov array overflowed
an ssize_t.
The readv() function may fail if:
EINVAL The iovcnt argument was less than or equal to 0, or greater
than {IOV_MAX}.
The following sections are informative.
Reading Data into an Array
The following example reads data from the file associated with the
file descriptor fd into the buffers specified by members of the
iov array.
#include <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>
...
ssize_t bytes_read;
int fd;
char buf0[20];
char buf1[30];
char buf2[40];
int iovcnt;
struct iovec iov[3];
iov[0].iov_base = buf0;
iov[0].iov_len = sizeof(buf0);
iov[1].iov_base = buf1;
iov[1].iov_len = sizeof(buf1);
iov[2].iov_base = buf2;
iov[2].iov_len = sizeof(buf2);
...
iovcnt = sizeof(iov) / sizeof(struct iovec);
bytes_read = readv(fd, iov, iovcnt);
...
None.
Refer to read(3p).
None.
read(3p), writev(3p)
The Base Definitions volume of POSIX.1‐2017, sys_uio.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 READV(3P)
Pages that refer to this page: sys_uio.h(0p), read(3p), writev(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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