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

# swab(3p)

swap bytes

## 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

swab — swap bytes

## SYNOPSIS

```
#include <unistd.h>
```

void swab(const void \*restrict *src*, void \*restrict *dest*,\
     ssize\_t *nbytes*);

## DESCRIPTION

The *swab*() function shall copy *nbytes* bytes, which are pointed to by *src*, to the object pointed to by *dest*, exchanging adjacent bytes. The *nbytes* argument should be even. If *nbytes* is odd, *swab*() copies and exchanges *nbytes*-1 bytes and the disposition of the last byte is unspecified. If copying takes place between objects that overlap, the behavior is undefined. If *nbytes* is negative, *swab*() does nothing.

## RETURN VALUE

None.

## ERRORS

No errors are defined.

*The following sections are informative.*

## EXAMPLES

None.

## APPLICATION USAGE

None.

## RATIONALE

None.

## FUTURE DIRECTIONS

None.

## SEE ALSO

The Base Definitions volume of POSIX.1‐2017, ***\<unistd.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 .