---
name: "vt_crc32"
section: "3tcl"
platform: "linux"
package: "tcllib"
version: "2.0+dfsg-4"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/vt_crc32"
---

# vt\_crc32(3tcl)

Crc32 transformation

```

```

## NAME

tcl::transform::crc32 - Crc32 transformation

## SYNOPSIS

package require **Tcl 8.6 9**

package require **tcl::transform::core ?1.1?**

package require **tcl::transform::crc32 ?1.1?**

**::tcl::transform::crc32** *chan* **-option** *value*...

```

```

## DESCRIPTION

The **tcl::transform::crc32** package provides a command creating a channel transformation which passes the read and written bytes through unchanged (like **tcl::transform::identity**), but additionally continuously computes the crc32 checksums of the data it has seen for each direction and stores them in Tcl variables specified at construction time. The checksum in question is zlib's crc32.

Related transformations in this module are **tcl::transform::adler32**, **tcl::transform::counter**, **tcl::transform::identity**, and **tcl::transform::observe**.

The internal **TclOO** class implementing the transform handler is a sub-class of the **tcl::transform::core** framework.

## API

- **::tcl::transform::crc32** *chan* **-option** *value*...

  This command creates a crc32 checksumming transformation on top of the channel *chan* and returns its handle. The accepted options are

  - **-read-variable** varname

    The value of the option is the name of a global or namespaced variable, the location where the transformation has to store the crc32 checksum of the data read from the channel.

    If not specified, or the empty string, the checksum of the read direction is not saved.

  - **-write-variable** varname

    The value of the option is the name of a global or namespaced variable, the location where the transformation has to store the crc32 checksum of the data written to the channel.

    If not specified, or the empty string, the checksum of the write direction is not saved.

## BUGS, IDEAS, FEEDBACK

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category *virtchannel* of the *Tcllib Trackers* \[http://core.tcl.tk/tcllib/reportlist\]. Please also report any ideas for enhancements you may have for either package and/or documentation.

When proposing code changes, please provide *unified diffs*, i.e the output of **diff -u**.

Note further that *attachments* are strongly preferred over inlined patches. Attachments can be made by going to the **Edit** form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.

## KEYWORDS

channel transformation, checksum, crc32, reflected channel, tip 230, transformation, virtual channel

## CATEGORY

Channels

## COPYRIGHT

```
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
```