DESCRIPTION

The purpose of this document is to show you how to call Perl subroutines directly from C, i.e., how to write callbacks.

Apart from discussing the C interface provided by Perl for writing callbacks the document uses a series of examples to show how the interface actually works in practice. In addition some techniques for coding callbacks are covered.

Examples where callbacks are necessary include

* An Error Handler

You have created an XSUB interface to an application's C API.

A fairly common feature in applications is to allow you to define a C function that will be called whenever something nasty occurs. What we would like is to be able to specify a Perl subroutine that will be called instead.

* An Event Driven Program The classic example of where callbacks are used is when writing an event driven program like for an X windows application. In this case you register functions to be called whenever specific events occur, e.g., a mouse button is pressed, the cursor moves into a window or a menu item is selected.

Although the techniques described here are applicable when embedding Perl in a C program, this is not the primary goal of this document. There are other details that must be considered and are specific to embedding Perl. For details on embedding Perl in C refer to the perlembed manpage.

Before you launch yourself head first into the rest of this document, it would be a good idea to have read the following two documents - the perlxs manpage and the perlguts manpage.