I have a framework (in C++) which is dependent on a few third party libraries. When I compile a static version of the library framework, no additional dependencies are needed, that is, the lib files of the third part libraries are not needed. When I compile the same framework as a DLL, additional dependencies are now needed otherwise I get linking errors. I can guess as to why this is happening but would like a concrete answer/explanation to understand what is happening.
EDIT: Just to clarify, I am developing a framework which can be compiled as a lib and as a dll and then used in a(n) (executable) project. When compiling the framework as a lib and using functions from a third party library, I don’t need additional dependencies. However, a project that now uses the lib file (which is the framework) must include the 3rd party lib files. When I compile the framework as a dll it gives me linking errors unless I specify the 3rd part libraries the framework is technically dependent on. For example: I have a few classes that call functionality from within Ogre3D. These classes are compiled as a lib file. I don’t need to link against OgreMain.lib when compiling a lib of the classes. On the other hand, when I am compiling a dll version of the same classes, I now need to link against OgreMain.lib
When you have a static library (a .lib file), which is just a collection of one or more object files (.obj), the linker just adds that code to yours in one executable. You can tell the linker to do this via a command line switch, an IDE configuration setting, or perhaps even a #pragma (specifics depend on your environment and compiler).
When you link in a DLL, you need to give the linker some code to call when you invoke one of the DLLs functions. Usually, this is done with a file of the same name as the .dll, save that it is a .lib. The code in that .lib is linked into your program the same way as described above, but when you call it, it loads the DLL (if not already loaded) and then invokes the proper function.
There are other ways to handle DLL linking (for instance, .def files or #using statements in .NET), but this seems to be what you’re talking about.
Responding to your question clarification:
The issue is that a .lib is not a final product. It is just an aggregation of object code to be used later when a linker connects all your functions calls to function addresses.
A DLL, on the other hand, is a final product, and so the linker requires all functions and variables be connected to actual addresses.
I’m speaking a bit imprecisely, but you get the idea.