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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.arch.embedded
Subject: Re: Static regex for embedded systems
Date: Tue, 21 Jan 2025 16:40:17 +0100
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On 21/01/2025 15:31, pozz wrote:
> Many times I need to parse/decode a text string that comes from an 
> external system, over a serial bus, MQTT, and so on.
> 
> Many times this string has a fixed syntax/layout. In order to parse this 
> string, I everytime create a custom parser that can be tedious, 
> cumbersom and error prone.
> 
> For example, suppose you have to decode a string from a modem that uses 
> AT commands. Many answers from the modem has the following schema:
> 
>    \r\n+<prefix>: <field1>,<field2>\r\n
>    \r\nOK\r\n
> 
> The prefix is known, the number and type of fileds are known too. With 
> regex, the parser would be simple.
> 

There are plenty of libraries for run-time regular expressions - they 
have been in the C++ standard library since C++11 (IIRC).  But run-time 
parsing of regex strings and matching for the input string will be very 
time and space costly in a small embedded system.  You want compile-time 
regular expression handling.

This had been planned for inclusion in C++23 (and therefore part of the 
current GNU ARM Embedded toolchain, if that's what you are using), but 
it didn't make it.  However, there are standalone compile-time regex 
libraries for C++ using templates and compile-time functions, which will 
in effect generate specialised parsers from the regex strings.