[//000000001]: # (tcl::transform::crc32 \- Reflected/virtual channel support)
[//000000002]: # (Generated from file 'vt\_crc32\.man' by tcllib/doctools with format 'markdown')
[//000000003]: # (Copyright &copy; 2009 Andreas Kupries <andreas\_kupries@users\.sourceforge\.net>)
[//000000004]: # (tcl::transform::crc32\(n\) 1 tcllib "Reflected/virtual channel support")

<hr> [ <a href="../../../../toc.md">Main Table Of Contents</a> &#124; <a
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# NAME

tcl::transform::crc32 \- Crc32 transformation

# <a name='toc'></a>Table Of Contents

  - [Table Of Contents](#toc)

  - [Synopsis](#synopsis)

  - [Description](#section1)

  - [API](#section2)

  - [Bugs, Ideas, Feedback](#section3)

  - [Keywords](#keywords)

  - [Category](#category)

  - [Copyright](#copyright)

# <a name='synopsis'></a>SYNOPSIS

package require Tcl 8\.6  
package require tcl::transform::core ?1?  
package require tcl::transform::crc32 ?1?  

[__::tcl::transform::crc32__ *chan* __\-option__ *value*\.\.\.](#1)  

# <a name='description'></a>DESCRIPTION

The __tcl::transform::crc32__ package provides a command creating a channel
transformation which passes the read and written bytes through unchanged \(like
__[tcl::transform::identity](identity\.md)__\), 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](adler32\.md)__,
__[tcl::transform::counter](vt\_counter\.md)__,
__[tcl::transform::identity](identity\.md)__, and
__[tcl::transform::observe](observe\.md)__\.

The internal __[TclOO](\.\./\.\./\.\./\.\./index\.md\#tcloo)__ class implementing
the transform handler is a sub\-class of the
__[tcl::transform::core](\.\./virtchannel\_core/transformcore\.md)__
framework\.

# <a name='section2'></a>API

  - <a name='1'></a>__::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\.

# <a name='section3'></a>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\.

# <a name='keywords'></a>KEYWORDS

[channel transformation](\.\./\.\./\.\./\.\./index\.md\#channel\_transformation),
[checksum](\.\./\.\./\.\./\.\./index\.md\#checksum),
[crc32](\.\./\.\./\.\./\.\./index\.md\#crc32), [reflected
channel](\.\./\.\./\.\./\.\./index\.md\#reflected\_channel), [tip
230](\.\./\.\./\.\./\.\./index\.md\#tip\_230),
[transformation](\.\./\.\./\.\./\.\./index\.md\#transformation), [virtual
channel](\.\./\.\./\.\./\.\./index\.md\#virtual\_channel)

# <a name='category'></a>CATEGORY

Channels

# <a name='copyright'></a>COPYRIGHT

Copyright &copy; 2009 Andreas Kupries <andreas\_kupries@users\.sourceforge\.net>