There are things that I don't understand when it comes to linking... I'm writing a program using a 3rd party library (the GEOS library). This program has a dependency to geos.lib but still needs geos.dll to run.
I read this question, I think I understand the difference between static and dynamic libraries. What I don't understand is why I still need a dll when I statically link a library.
It's not statically linked. The .lib is just a stub library that binds in the .dll on windows. That is, you link with the .lib at compile time, and then at runtime it will go looking for the .dll.
There are 3 kinds of libraries on Windows:
object libraries are statically linked. They contain the full object definitions of the code abstracted by the library.
import libraries is a special form of an object library. Instead of containing code they contain information for the linker that ultimately maps the executable file to the dynamic-link library.
dynamic link libraries, like object libraries, supply code for your program. However, this code is loaded at runtime and not compiled into your exe.
You don't always need to link an import library. Instead you can call LoadLibrary() and lookup the API entry points by name or ordinal. (You always have to tell the code which DLL and where in that DLL's API you want to enter.)
The other comments here are correct in that you cannot make a DLL into a static lib without recompiling the code for the libary -- it is a different kind of output.
If .lib was created by Visual Studio then check value of Project properties -> Linker -> Input -> Module Definition File. If it's not empty then link.exe create stub library instead of static library even if Project properties -> General -> Configuration Type is "Static library (.lib)".
You are definetely linking to a dynamic library. Just because the linker requires .lib file doesn't mean you're linking to a static library.
You can statically link the lib file if and only if this is a static lib file. So first you need to convert your dll's project to the static lib, build it and after that use the product of your build which will be a static .lib file.
