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Table 4-1. Preprocessor directives
Preprocessor directive Action
#define symbol Defines symbol
#undef symbol Undefines symbol
#if symbol [operator symbol2]... symbol to test; operators are ==, !=, &&, and || followed by
#else, #elif, and #endif
#else Executes code to subsequent #endif
#elif symbol [operator symbol2] Combines #else branch and #if test
#endif Ends conditional directives
#warning text text of the warning to appear in compiler output
#error text text of the error to appear in compiler output
#line [ number ["file"] | hidden] number specifies the line in source code; file is the filename to
appear in computer output; hidden instructs debuggers to skip over
code from this point until the next #line directive
#region name Marks the beginning of an outline
#end region Ends an outline region
Conditional Attributes
An attribute decorated with the Conditional attribute will be compiled only if a given
preprocessor symbol is present. For example:
// file1.cs
#define DEBUG
using System;
using System.Diagnostics;
[Conditional("DEBUG")]
public class TestAttribute : Attribute {}
// file2.cs
#define DEBUG
[Test]
class Foo
{
[Test]
string s;
}
The compiler will not incorporate the [Test] attributes if the DEBUG symbol is in
scope for file2.cs.
Pragma Warning
The compiler generates a warning when it spots something in your code that seems
unintentional. Unlike errors, warnings don’t ordinarily prevent your application
from compiling.
Preprocessor Directives | 175
Advanced C#