I am new to Visual C++, but have been using FoxPro since the mid-nineteen-eighties and have just discovered how to build a DLL in Visual C++ ver. 5.0 that I can access in Visual FoxPro 5.0a with a "SET LIBRARY TO filename.dll" command. It seems to load fine and behaves normally for a while and then I get a General Protection Fault error "Invalid Page Fault error in KERNEL32.DLL at 0137:bff78040" It is always the same error at the same address.
My DLL performs processing on strings. I use the FoxPro API memory handle locking and unlocking function calls within the DLL before performing the string processing using pointers. The FoxPro application simply opens a file, reads from it and performs string processing using the DLL then displaying the string. Then it performs the reverse of the process, writing the changes back to the file. The program seems to behave correctly for a while and then the GPF occurs.
The DLL was created as a "Win32 DLL" (non-MFC) in Visual C++ 5.0 I followed the instructions included with Visual FoxPro for Visual C++ 4.0 setting the C code compiler to _fastcall and "Multi-threaded DLL." Is there some other configuration setting that I have to change for compiling a DLL for VFP in VC++ 5.0?