Character Class Search Explainer Tool

2020-06-12 - By Robert Elder

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This article is part of Series On Regular Expressions.

About This Visualization Tool

The purpose of this visualization tool is to clearly illustrate how regular expression character classes work. By demonstrating that character classes can be thought of as a simple list of acceptable characters to match, this visualization tool shows a concrete description of what a character class actually represents. The C source code above shows an equivalent representation of the specified search string that may contain almost any character class that you'd find in a typical regular expression. Currently, this tool supports many common character classes such as typical ranges like '[a-z]', or '[0-9]'. Other character class features such as class negation, hexadecimal ranges, escaped classes and several common escaped ASCII character are also supported. The input forms above can be changed to dynamically update the equivalent C code.

Caveats

This tool works by using a custom-written regular expression engine that is fairly complete, but still lacks support for a few significant features such as Unicode. Check out Regular Expression Test Cases and An LL Grammar For Regular Expression Parsing for more information.

Another consideration is that real regular expression engines don't loop through a long list of characters as the C source code above might imply. The C code is intended to be functionally correct rather than as efficient as possible. This tool could have been written to produce C code that was as efficient as possible, however this would make it more complicated which would completely defeat its purpose as an educational tool.

This article is part of a Series On Regular Expressions.

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