Pointers and Arrays in C# - Preprocessor Directives
(Page 4 of 4 )
Preprocessor directives supply the compiler with additional information about regions of code. The most common preprocessor directives are the conditional directives, which provide a way to include or exclude regions of code from compilation. For example:
#define DEBUG
class MyClass
{
int x;
void Foo()
{
# if DEBUG
Console.WriteLine("Testing: x = {0}", x);
# endif
}
...
}
In this class, the statement inFoois compiled as conditionally dependent upon the presence of theDEBUGsymbol. If we remove theDEBUGsymbol, the statement is not compiled. Preprocessor symbols can be defined within a source file (as we have done), and they can be passed to the compiler with the/define:symbol command-line option.
The#errorand#warningsymbols prevent accidental misuse of conditional directives by making the compiler generate a warning or error given an undesirable set of compilation symbols. See Table 4-3 for a list of preprocessor directives and their actions.
Table 4-3. Preprocessor directives and their actions Preprocessor directive | Action |
#define symbol | Defines symbol. |
#undef symbol | Undefines symbol. |
#if symbol [operator symbol2] ... | symbolto test. |
| | operators are ==, !=, &&, and ||followed by #else, #elif, and #endif. |
#else | Executes code to subsequent #endif. |
#elif symbol [operator symbol2] | Combines #elsebranch and #iftest. |
#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] | numberspecifies the line in source code; fileis the file-name to appear in computer output; hiddenspecifies that the compiler should generate debugger information (this feature was added in Visual C# 2003). |
#region name | Marks the beginning of an outline. |
#end region | Ends an outline region. |
Please check back next week for the conclusion to this article.
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 This article is excerpted from chapter four of C# 3.0 in a Nutshell, Third Edition, A Desktop Quick Reference, written by Joseph Albahari and Ben Albahari (O'Reilly; ISBN: 0596527578). Check it out today at your favorite bookstore. Buy this book now.
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