API Programming Series #1

Since these functions are encapsulated within external DLLs they are not available in VB by default. Before invoking (i.e. using) them, we must declare them. Usually this is done in the General | Declarations part of the module in which they are to be used.

One important thing should be remembered while declaring API functions within a form module. VB does not allow public Declare statements within form modules. So the Declare statements should be explicitly specified as Private since all object module members are considered Public by default. But this makes them invisible outside the module in which they are defined. So the functions should be declared in every module that needs to use them.
Declaring them in a separate .BAS module where they can be declared as Public and are therefore accessible to all the modules eliminates this duplication. This also permits easier maintenance.

Note: We will see how to declare and use API functions in the second article of this series.