Programming with the XForms Library
If you're already thinking ahead to greater things, you are probably a little confused about how to get an XForms application to do anything other than return after a single button is pushed. The next programming example provides a hint, but the whole story will have to wait for the next two articles in the series.
The basic idea is to proceed as in the xhello example, but to add some functionality to each action. We do this by creating a multi-lingual “Hello World” program called xmulti. The source is shown in Listing 2, and is also available on the series web page. Save this file as xmulti.c. It should compile with the command:
gcc -lX11 -lforms -lm xmulti.c -o xmulti
The program can now be executed by typing xmulti, and should look like the example shown in Figure 2. Examination of the xmulti source code reveals the fundamental steps involved in creating an XForms program are as follows:
Include forms.h to access the XForms routines
Call fl_initialize() as soon as possible
Set up your graphical interface by creating forms
Assign actions to relevant objects by setting callbacks
Show one or more forms
Turn control over to fl_do_forms()
The only thing new here is point 4, which our original xhello program did not include. In xmulti, the English and French buttons are set to call the routine set_language(), which changes the display. But the basic idea is very general, and you can easily add buttons, menus, etc., that call complicated functions, display other forms, or what have you.
Next month, we'll expand on this basic discussion by writing a more complicated program. This will involve using menus, multiple windows, and a few other refinements. By the time we've done the third article, you should be well on your way to creating useful applications.
If you can't wait to learn more, then you may want to start reading through the XForms manual. Browsing the example applications' source code is also an excellent way to familiarize yourself with the XForms way of doing things.
Thor Sigvaldason is the author of the statistics program xldlas, which uses the XForms library (see Linux Journal, Issue 34, February 1997). He is trying to complete a PhD in economics, and can be reached at email@example.com.
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