C# 4 and .NET 4

The C# Preprocessor Directives ❘ 55
< summary >
The Add method allows us to add two integers.
< /summary >
< returns > Result of the addition (int) < /returns >
< param name="x" > First number to add < /param >
< param name="y" > Second number to add < /param >
< /member >
< /members >
< /do c >
code snippet MathLibrary.xml
Notice how the compiler has actually done some work for you; it has created an element and
also added a < member > element for each type or member of a type in the fi le. Each element has a
name attribute with the full name of the member as its value, prefi xed by a letter that indicates whether this
is a type ( T: ), fi eld ( F: ), or member ( M: ).
The C# PreProCessor direCTiVes
Besides the usual keywords, most of which you have now encountered, C# also includes a number of
commands that are known as preprocessor directives. These commands never actually get translated to
any commands in your executable code, but instead they affect aspects of the compilation process. For
example, you can use preprocessor directives to prevent the compiler from compiling certain portions of
your code. You might do this if you are planning to release two versions of the code — a basic version and
an enterprise version that will have more features. You could use preprocessor directives to prevent the
compiler from compiling code related to the additional features when you are compiling the basic version of
the software. Another scenario is that you might have written bits of code that are intended to provide you
with debugging information. You probably don ’ t want those portions of code compiled when you actually
ship the software.
The preprocessor directives are all distinguished by beginning with the # symbol.
C++ developers will recognize the preprocessor directives as something that plays an
important part in C and C++. However, there aren ’ t as many preprocessor directives
in C#, and they are not used as often. C# provides other mechanisms, such as custom
attributes, that achieve some of the same effects as C++ directives. Also, note that C#
doesn ’ t actually have a separate preprocessor in the way that C++ does. The so - called
preprocessor directives are actually handled by the compiler. Nevertheless, C# retains
the name preprocessor directive because these commands give the impression of a
preprocessor.
The next sections briefl y cover the purposes of the preprocessor directives.
#define and #undef
#define is used like this:
#define DEBUG
What this does is tell the compiler that a symbol with the given name (in this case DEBUG ) exists. It is a little
bit like declaring a variable, except that this variable doesn ’ t really have a value — it just exists. And this
symbol isn ’ t part of your actual code; it exists only for the benefi t of the compiler, while the compiler is
compiling the code, and has no meaning within the C# code itself.
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