Changes from API V1 (The GNU Awk User’s Guide)

From Get docs

17.4.15 Changes From Version 1 of the API

The current API is not binary compatible with version 1 of the API. You will have to recompile your extensions in order to use them with the current version of gawk.

Fortunately, at the possible expense of some compile-time warnings, the API remains source-code–compatible with the previous API. The major differences are the additional members in the awk_ext_func_t structure, and the addition of the third argument to the C implementation function (see section Registering An Extension Function).

Here is a list of individual features that changed from version 1 to version 2 of the API: