Building a VFP DLL

Building the DLL is little different from the regular process of building a FoxPro executable. Create a new project and add the program which defines the class to this project. Click the Build button on the Project Manager but then select Single-threaded COM server instead of the "executable" option.

The build process will create an in-process COM server as vfpcustomer.dll and will also create the Type Library file (vfpcustomer.tlb) and the Registration Information file (vfpcustomer.vbr). You'll need all three when you come to distribute the system.

The final option on the Project Manager's Build Options dialog is for a Multi-threaded COM server. This can give better performance on a system with multiple processors but requires more thought and is probably not worthwhile on something that is just an intermediate stage in the migration.

Register the DLL

In order to make the new FoxPro DLL available to external programs you need to register it with Windows. The easiest way to do this is to run the RegSvr32 command from the Windows command line. You should get the simple message box as shown here on the left to show that the DLL has been registered successfully.

These examples come from Windows XP. If you are running Windows 7 then you must run regsvr32 as an administrator.

Select All Programs and then Accessories then right-click on Command Prompt and select Run as administrator. If you forget to do this then you will get an message quoting error number 0x80070005. A search on the web for this error will show that many people have made the same mistake.

If the process fails under XP then you'll get a less helpful message like the one below. The problem is usually that the name or the path to the file is wrong.

The next steps

The first two steps in this process were to write and test a DLL in VFP. The final step is to call it from Visual Basic or C#.