Re: Static regex for embedded systems

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.