2.3 Methods

Although you haven't seen the class initializer for Media yet, you can now see how to define a simple method. Here are some important things to remember about methods:

Methods usually do not appear in class structure. Instead, method prototypes usually appear somewhere soon after the class structure.
A method's name should reflect the class name (for example, media_*() for Media ).
A method's first parameter is always an object (a structure of the instance class). Any remaining parameters are up to you.
In public methods, always check that the first parameter is actually a valid object of the method's class.
In addition, cast this object parameter after you do the check, because the object you get could be in a subclass.
Be careful about setting an object's attributes. Standard GTK+/GNOME practice dictates that all attributes are properties (see Section 2.4); use that system for setting attributes.

These considerations sound like a lot of fuss, but this example shows that it doesn't amount to much:

 void media_print_inv_nr(Media *object) {   Media *media;   g_return_if_fail(IS_MEDIA(object));   media = MEDIA(object);   g_print("Inventory number: %d\n", media->inv_nr); }

Most public methods contain everything here but the last line ( g_print(...); ).