Im trying to call a Windows API, but the linker gives an unresolved external error (LNK2001) on the API name. Why?
When you call a function whose code is not in your program itself, such as any Windows API, you need to tell the linker where the function is so it can store information about the function in your EXE. This is done with an import library. An import library is a LIB file that contains the list of functions exported from its corresponding DLL. For example, kernel32.lib contains the exports for kernel32.dll. When Windows loads your EXE, it reads this information, loads the correct DLL, and resolves the function calls. The VC AppWizard creates projects with the most commonly-used LIBs (such as kernel32.lib, user32.lib, etc.) already listed in the linker options, but if you use call APIs in other DLLs, you’ll need to add the corresponding LIB files. Let’s take for example the API PathAddBackslash(). When you get an unresolved external error on this API, you need to find out which LIB file its definition is contained in. Read the MSDN page on PathAddBackslash(), and at the bottom you’ll see:
