class definition and implementation in C# vs C++

With C++, I can have one class definition in a header file, and have a multiple implementation files by including the header file.

With C#, it seems that there is no such header file, as one class should contain both d开发者_如何转开发efinition/implementation.

I wonder if the number of lines can be very big, because one can't separate the class into multiple files. Am I correct? I mean, in some cases, one can't change the class design to have smaller classes. In this case, is there a way to solve this problem?

You can separate a class into multiple files using the partial keyword

public partial class ClassNameHere
{
}

It is possible to split the definition of a class or a struct, or an interface over two or more source files using the Partial keyword modifier Link to msdn with the partial class

Partial classes only give you so much. There is still no way, that i know of, to split your class definition from implementation, such that each exists in a separate file. So if you like to develop based on a need-to-know paradigm then you are sort of stuck. Basically there are three levels a developer can work at...

1) Owns all the code and has access to, and maintains all of it.

2) Wishes to use some useful base class(s) which may form part of a framework, or may just be a useful class with some virtual methods, etc, and wishes to extend, or re-implement some virtual base class methods of interest. Now the developer should not need to go and look at the code in the base class(s) in order to understand things at a functional level. If you understand the job of a function, it's input and output parameters, there is no need to go and scratch inside source code. If you think there's a bug, or an optimization is needed, then refer to the developer from 1) who owns and maintains the base code. Of course there's nothing saying that 1) and 2) cannot be associated with the same developer, in which case we have no problem. In fact, this is more than often the case i suspect. Nevertheless, it is still good practice to keep things well separated according to the level at which you are working.

3) A developer needs to use an already packaged / sealed object / component dll, which exposes the relevant interfaces.

Within the context of c#, 1) and 3) have no problems. With 2) i believe there is no way to get round this (unless you change from exposing virtual base methods to exposing interface methods which can be reimplemented in a component owning the would-be base class). If i want to have a look at a class definition to browse over the methods, scaffolding functions, etc, i have to look at a whole lot of source code as well, which just gets in the way of what i am trying to focus on.

Of course if there is class definition documentation external to how we normally do it ( in headers and source files), then i must admit, that within the context of 2), there is not reason to ever look into a class definition file to gain functional knowledge.

So maybe clever Tom's came up with c#, decided to mix class definition with implementation in an attempt to encourage developers to have external documents for their class definitions, and interfaces, which in most IT companies is severely lacking.

Use a partial class as @sparks suggests, or, split into several classes. It's a good rule of thumb that, if you can't fit a class onto a couple of pages, it's complicated enough to need breaking apart.