Include everything, Separate with "using"

Question

I'm developing a C++ library. It got me thinking of the ways Java and C# handle including different components of the libraries. For example, Java uses "import" to allow use of classes from other packages, while C# simply uses "using" to import entire modules.

My questions is, would it be a good idea to #include everything in the library in one massive include and then just use the using directive to import specific classes and modules? Or would this just be down right crazy?

EDIT: Good responses so far, here are a few mitigating factors which I feel add to this idea:

1) Internal #includes are kept as normal (short and to the point)
2) The file which includes everything is optionally supplied with the library to those who wish to use it
3) You could optionally make the big include file part of the pre-compiled header

Answer 1

You're confusing the purpose of #include statements in C++. They do not behave like import statements in Java or using statements in C#. #include does what it says; namely, loads and parses the entire indicated file as part of the current translation unit. The reason for the separate includes is to not have to spend compilation time parsing the entire standard library in every file. In contrast, the statements you're trying to make #include behave like are merely for programmer organization purposes.

#include is for management of the compilation process; not for separating uses. (In fact, you cannot use seperate headers to enforce seperate uses because to do so would violate the one definition rule)

tl;dr -> No, you shouldn't do that. #include as little as possible. When your project becomes large, you'll thank yourself when you're not waiting many hours to compile your project.

Answer 2

I would personally recommend only including the headers when you need them to explicitly show which functionalities your file requires. At the same time, doing so will prevent you from gaining access to functionalities you might no necessarily want, e.g functions unrelated to the goal of the file. Sure, this is no big deal, but I think that it's easier to maintain and change code when you don't have access to unnecessary functions/classes; it just makes it more straightforward.