The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> readv - read a vector

#### SYNOPSIS

> ``[XSI] #include <sys/uio.h>
> ssize_t readv(int` fildes`, const struct iovec *`iov`, int` iovcnt`);``
> `
> `

#### DESCRIPTION

> 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.

#### RETURN VALUE

> Refer to read.

#### ERRORS

> Refer to read.

> 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.

#### EXAMPLES

> ##### 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);
>     ...

#### APPLICATION USAGE

> None.

#### RATIONALE

> Refer to read.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> read, writev

> XBD <sys/uio.h>

#### CHANGE HISTORY

> First released in Issue 4, Version 2.

#### Issue 6

> Split out from the read() reference page.

#### Issue 7

> Changes are made related to support for finegrained timestamps.

End of informative text.

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