Datasheet

Part I: The C# Language

Managed Code

The role of the CLR doesn ’ t end once you have compiled your code to MSIL, and a JIT compiler has

compiled that to native code. Code written using the .NET Framework is managed when it is executed

(a stage usually referred to as runtime ). This means that the CLR looks after your applications by

managing memory, handling security, allowing cross - language debugging, and so on. By contrast,

applications that do not run under the control of the CLR are said to be unmanaged, and certain languages

such as C++ can be used to write such applications, which, for example, access low - level functions of the

operating system. However, in C# you can write only code that runs in a managed environment. You will

make use of the managed features of the CLR and allow .NET itself to handle any interaction with the

operating system.

Garbage Collection

One of the most important features of managed code is the concept of garbage collection . This is the .NET

method of making sure that the memory used by an application is freed up completely when the

application is no longer in use. Prior to .NET this was mostly the responsibility of programmers, and a

few simple errors in code could result in large blocks of memory mysteriously disappearing as a result of

being allocated to the wrong place in memory. That usually meant a progressive slowdown of your

computer followed by a system crash.

.NET garbage collection works by inspecting the memory of your computer ever so often and

removing anything from it that is no longer needed. There is no set time frame for this; it might happen

thousands of times a second, once every few seconds, or whenever, but you can rest assured that it

will happen.

There are some implications for programmers here. Because this work is done for you at an

unpredictable time, applications have to be designed with this in mind. Code that requires a lot of

memory to run should tidy itself up, rather than wait for garbage collection to happen, but that isn ’ t as

tricky as it sounds.

Fitting It Together

Before moving on, let ’ s summarize the steps required to create a .NET application as discussed

previously:

1. Application code is written using a .NET - compatible language such as C# (see Figure 1 - 1 ).

C#code

Figure 1-1

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