请问遇到这种问题如何解决
Compiling...
Exer31.cpp
Linking...
Exer31.obj : error LNK2001: unresolved external symbol "long __stdcall WndProc(struct HWND__ *,unsigned int,unsigned int,long)" (?WndProc@@YGJPAUHWND__@@IIJ@Z)
Debug/Exer31.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.
Exer31.exe - 2 error(s), 0 warning(s)
