C ++，Visual Studio 2012，LIB，DLL，包含，源和链接器

Question

I'm trying to understand what exactly all of these are and how they relate to each other (and most importantly, how to install them).

From what I've read, LIBs are libraries linked during the compilation of my project and DLLs are libraries linked during the runtime of my project.

So for me to use a LIB , I have to have the actual .LIB file somewhere in my computer, go to Project -> Properties -> VC++ Directories and add the path to the file in the Library Directories , and after this I have to go to Linker -> Input -> Additional Dependencies add the .lib name in there, and finally I need to type #include in my code, right?

So, some questions:

1. When I finish and build the release of my program, will the .exe only run if the target platform has the .lib installed in their PC as well? If yes, what steps do I need to do to make sure the .lib goes with the .exe?

2. When I get the source of a open source project, if I add them (using Add Existing Item... ) to my project, can I use them just by using #include as if the files were mine and it would be the same as having the .lib installed? Or do I need to install the .lib file and still use these source files?

3. I have a project using OpenGL and I linked to glew32.lib , but I don't have the lib or any new directory added in the VC++ Directories , so I think this means I must've installed the .lib in the system folder or somewhere where the Visual Studio won't ask for another directory, should I worry about this when releasing a project?

4. How the above questions relate to DLLs and is there any reason why should I use DLLs over LIBs or the other way around?

I'm starting to use more and more libraries and I noticed I just dragged, copied and included it everywhere so I could use them but never really understood how they "fit" in the project. Especially those open source libraries where they provide so many files and I don't really know what to do with them...

Answer 1

1. You don't need to have LIB files along with your EXE file for running in another computer, LIB files are static files and DLL files are dynamic. So when you compile all static codes will be included in your EXE file, but DLL files will be loaded and used dynamically in runtime, so you just need to have your DLL files with your EXE file. This way, your code will work and run properly in other computers.

2. Just adding another project is not enough, you need to compile them and generate LIB files out of them. Then you add the generated LIB file to your final project and include external projects in your final binary. If you are compiling multiple projects together in a solution, you'll need to set project build order in solution properties in VS.

3. No, that's OK. It seems you've put LIB files in right folder and you don't need to have LIB file with your EXE file to run it in other computers.

4. DLLs are dynamic libraries, so you need to have them with your application. Installers usually install EXE files with DLL files in the same folder, so your app will run properly, but no need to include LIB files at all.

Also you can include LIB files like this:

#pragma comment(lib, "glew32.lib")

So you don't need to do it in project settings, but assuming you have your LIB file in "Library Directories" path.

Using DLL files can be done in two ways: One is linking your application to DLL file and having DLL file's function entry in your EXE file's import table: like using

#include <windows.h>

then

GetWindowsDirectory(windir, MAX_PATH);

So you'll have GetWindowsDirectory API entry in your EXE file's Import Table .

Also you can do it dynamically:

hinstDLL = LoadLibrary("kernel32.dll");
if (hinstDLL != NULL)
{
    func_GetWindir = (DLLPROC) GetProcAddress(hinstDLL, "GetWindowsDirectoryA");
...

There is not much difference, only difference is: In first method, as it's in your EXE file's Import Table, if there was no kernel32.dll or there was no GetWindowsDirectory entry in kernel32.dll , your EXE will not run at all, it will show a critical error and will not run. But in dynamic way (second way), your app will run, but as soon as your code try to use GetWindowsDirectoryA API, it will fail. You will have 0x00 in func_GetWindir . If you attempt to call it, then program will crash.