---
name: "readv"
section: "3p"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/readv/3p"
---

# readv(3p)

read a vector

## PROLOG

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.

## NAME

readv — read a vector

## SYNOPSIS

```
#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()*

The Base Definitions volume of POSIX.1‐2017, ***\<sys\_uio.h\>***

## COPYRIGHT

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 .