From Get docs

17.4 API Description

C or C++ code for an extension must include the header file gawkapi.h, which declares the functions and defines the data types used to communicate with gawk. This (rather large) section describes the API in detail.

Extension API Functions Introduction    Introduction to the API functions.
General Data Types    The data types.
Memory Allocation Functions    Functions for allocating memory.
Constructor Functions    Functions for creating values.
Registration Functions    Functions to register things with


Printing Messages    Functions for printing messages.
Updating ERRNO    Functions for updating ERRNO.
Requesting Values    How to get a value.
Accessing Parameters    Functions for accessing parameters.
Symbol Table Access    Functions for accessing global


Array Manipulation    Functions for working with arrays.
Redirection API    How to access and manipulate


Extension API Variables    Variables provided by the API.
Extension API Boilerplate    Boilerplate code for using the API.
Changes from API V1    Changes from V1 of the API.