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Some of the MS-Windows API functions require call backs. A call back is a pointer to the user-defined function, to which MS-Windows API functions should return information. This requires a lower-level language and products like PowerBuilder is not capable of providing pointers to an user defined function. Basically, you can call MS-Windows API functions or other DLL's from your code, but vice-versa is not possible.
For a higher level language like PowerScript to interface with MS-Windows API functions, call back is required. For this, a custom DLL which acts as a wrapper for that API function must be developed. This wrapper DLL sets up its own routine for the call back and calls the MS-Windows API function for you. This function should be able to accept parameters from you and give back data returned from the MS-Windows API function.
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