The primary data structure1 in awk is the associative array (see Arrays). Extensions need to be able to manipulate awk arrays. The API provides a number of data structures for working with arrays, functions for working with individual elements, and functions for working with arrays as a whole. This includes the ability to “flatten” an array so that it is easy for C code to traverse every element in an array. The array data structures integrate nicely with the data structures for values to make it easy to both work with and create true arrays of arrays (see General Data Types).
 Okay, the only data structure.