Advanced PowerBuilder

Dynamic Link Libraries

As we mentioned earlier, creating a C++ user object involves linking your PowerBuilder application to a MS-Windows DLL (dynamic link library), which is a set of functions. You can create your own DLLs to extend the capabilities of the base libraries of any MS-Windows application. A MS-Windows application calls DLLs only at run time. This helps reduce the size of your EXE file. It also makes your MS-Windows application modular in nature-you can reuse the same DLLs across several different MS-Windows applications, thus saving you valuable time and memory space.

MS-Windows comprises three main DLLs: GDI32.dll, User32.dll and Kernel32.dll. These are the basic set of functions for the MS-Windows operating system, though they are only a tiny subset of all the system DLLs provided by MS-Windows. They are also supported by other file types; for example, Krnl386.exe supports the Kernel32.dll. Other common libraries that can be found on most systems include Winmm.dll (multimedia extensions) and advapi32.dll for manipulating the system registry. The default location for these DLLs is the System subdirectory of your Windows directory (ie. C:\Windows\System).

You can also create your own DLL's that will carry out specific tasks required for your application. As we mentioned earlier, these will typically be complex functions that would be too slow to do in PowerScript. Other times, you may feel the need to write your own DLLs for wrappers. A wrapper function is used to access some of the underlying MS-Windows DLL functions that would not normally be available to PowerScript. You could create a wrapper to use this otherwise forbidden function and present it to your PowerScript in a useable form.

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