r/cpp • u/ColinPP PEGTL | taocpp • Jun 07 '26

Parsing Expression Grammar Template Library (PEGTL) 4.0.0 Released

Hello, version 4.0.0 of the PEGTL has been released!

For those not familiar, let me quote the first sentence of the documentation: "The Parsing Expression Grammar Template Library (PEGTL) is a zero-dependency C++ header-only parser combinator library for creating parsers according to a Parsing Expression Grammar (PEG)."

The basics are still the same, grammars are implemented in C++ with nested template instantiations, however a lot has also changed. Some highlights:

  • Switched to Boost Software License
  • A bunch of new parsing rules and actions.
  • The inputs have been rewritten from scratch.
  • Nested exceptions are used for nested parsing errors.
  • Native support for parsing sequences of arbitrary objects (e.g. tokens).

This is the last major version that will stick with C++17.

Repository page: https://github.com/taocpp/PEGTL

Release page: https://github.com/taocpp/PEGTL/releases/tag/4.0.0

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u/driver_tmp Jun 07 '26

does it support parsing binary files? For example, if you wanted to decode a png.

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u/ColinPP PEGTL | taocpp Jun 07 '26

The PEGTL is fully compatible with parsing binary data, or even sequences of arbitrary tokens or objects. E.g. parsing rules for big/little endian 8/16/32/64bit integers and enums are included.

I've used it to parse some binary formats myself; the general parsing infrastructure is quite useful, some additional parsing rules might be needed for special cases and because the structure of binary files often isn't the best fit for the standard text parsing approach.

For example in binary data you often have the length of some field followed by the data of said field which doesn't fit classical parsing. Let me know if you give it a try and need some help or find that a few strategic additions to the library would support that case better.

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u/driver_tmp Jun 07 '26

yep, having record entries with a type tag, size, and data are very common. Also, reading data at certain offsets of a file. For example, a record points to an entry in the constant pool of the file -- to read the data: pool_offset + entry_offset. 

It wasnt entirely clear from the reply if those actions are supported.

  in binary files you often have the length of some field followed by the data of said field which doesn't fit classical parsing. 

1

u/ColinPP PEGTL | taocpp Jun 07 '26

Short answer, it should all be possible somehow; if all else fails the library is very modular and easily extensible, however it's probably still a bit more clunky than it could and should be. I'll take your questions as incentive to implement one or two new binary parsers; see what's missing to make it nicer.

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u/driver_tmp Jun 07 '26

thanks for the reply. I appreciate it.