C# 4 and .NET 4

The C# Preprocessor Directives ❘ 57
// do something else
#else
// code for the leaner version
#endif
Note that, unlike the situation in C++, using #if is not the only way to compile code
conditionally. C# provides an alternative mechanism through the Conditional attribute,
which is explored in Chapter 14, “ Refl ection. ”
#if and #elif support a limited range of logical operators too, using the operators ! , == , != , and || . A
symbol is considered to be true if it exists and false if it doesn ’ t. For example:
#if W2K & & (ENTERPRISE==false) // if W2K is defined but ENTERPRISE isn't
#warning and #error
Two other very useful preprocessor directives are #warning and #error . These will respectively cause
a warning or an error to be raised when the compiler encounters them. If the compiler sees a #warning
directive, it will display whatever text appears after the #warning to the user, after which compilation
continues. If it encounters a #error directive, it will display the subsequent text to the user as if it were
a compilation error message and then immediately abandon the compilation, so no IL code will be
generated.
You can use these directives as checks that you haven ’ t done anything silly with your #define
statements; you can also use the #warning statements to remind yourself to do something:
#if DEBUG & & RELEASE
#error "You've defined DEBUG and RELEASE simultaneously!"
#endif
#warning "Don't forget to remove this line before the boss tests the code!"
Console.WriteLine("*I hate this job.*");
#region and #endregion
The #region and #endregion directives are used to indicate that a certain block of code is to be treated as
a single block with a given name, like this:
#region Member Field Declarations
int x;
double d;
Currency balance;
#endregion
This doesn ’ t look that useful by itself; it doesn ’ t affect the compilation process in any way. However, the real
advantage is that these directives are recognized by some editors, including the Visual Studio .NET editor.
These editors can use these directives to lay out your code better on the screen. You will see how this works
in Chapter 16.
#line
The #line directive can be used to alter the fi lename and line number information that is output by the
compiler in warnings and error messages. You probably won ’ t want to use this directive that often. It ’ s most
useful when you are coding in conjunction with some other package that alters the code you are typing
in before sending it to the compiler. In this situation, line numbers, or perhaps the fi lenames reported by
the compiler, won ’ t match up to the line numbers in the fi les or the fi lenames you are editing. The #line
www.it-ebooks.info