why do game engines prefer static libraries over dynamic link libraries

Question

I've been reading a few gaming books. And they always prefer to create the engine as a static library over dynamic link. I am new to c++ so I am not highly knowledge when it comes to static libraries and dynamic link libraries. All I know is static libraries increase the size of your program, where DLL link libraries are loaded as you need them within your program.

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I've played games where it almost seemed they used DLL's to load in sound, lighting, and what not all individually. as the level was loading up. cause you don't necessarily need that when your at the game menu.

Answer 1

Dynamic link libraries need to be position independent; this can cause performance inefficiencies on some processor architectures.

Static libraries can be optimized when included in your program, e.g., by stripping dead code. This can improve cache performance.

Answer 2

By position independent, he means that since the game engine and DLL are completely separated, the DLL is stand-alone and cannot be interwoven into the game engine code, whereas statically linking a library allows the compiler to optimize using both your game engine code AND the library code.

For example, say there's a small function that the compiler thinks should be inlined (copied directly in place of a function call). Then with a static library, the compiler would be able to inline this code, since it knows what the code is (you're linking at compile-time). However, with a dynamic library, the compiler would be unable to inline that code, since it does not know what the code is (since it will be linking at run-time).

Answer 3

Another question covers the differences between static and dynamic libraries: http://stackoverflow.com/questions/140061/when-to-use-dynamic-vs-static-libraries

As for why they use static libraries, the extra speed may be worth it and you can avoid DLL hell (was a big problem in the past). It's also useful if you want to distribute your program and libraries together, ensuring the recipient has the correct dependencies, though there's nothing stopping you from distributing DLLs together with the executable.

Answer 4

Another often overlooked reason which deserves mention is that for many games you aren't going to be running lots of other stuff, and many libraries that are used for games aren't going to be used for the other things that you may be running at the same time as a game, so you don't have to worry about one of the major positives you get from using shared libraries, which is that only one copy of (most of) the library needs to loaded at one time while several things can make use of that one copy. When running a game you will probably only have one program that would want to use that library running anyway because you probably aren't going to be running many other programs (particularly other games or 3D programs) at the same time.

You also open up the possibility of global/link time optimization, which is much more difficult with shared libraries.

Answer 5

When developing games for a console, often dynamic linking isn't an option. If you want to use the engine for both console and PC development, it would be best to avoid dynamic linking.