Margaret Rouse is an award-winning technical writer and teacher known for her ability to explain complex technical subjects simply to a non-technical, business audience. Over…
Preprocessor directives are lines included in a program that begin with the character #, which make them different from a typical source code text. They are invoked by the compiler to process some programs before compilation. Preprocessor directives change the text of the source code and the result is a new source code without these directives.
Although preprocessing in C# is conceptually similar to that in C/C++, it is different in two aspects. First, preprocessing in C# does not involve a separate step for preprocessor execution before compilation. It is processed as a part of the lexical analysis phase. Second, it cannot be used to create macros. In addition, the new directives #region and #unregion have been added in C# along with the exclusion of some directives used earlier (#include is a notable directive whose use is replaced with "using" to include assemblies).
Java does not support preprocessor directives.
A preprocessor directive is usually placed in the top of the source code in a separate line beginning with the character "#", followed by directive name and an optional white space before and after it. Because a comment on the same line of declaration of the preprocessor directive has to be used and cannot scroll through the following line, delimited comments cannot be used. A preprocessor directive statement must not end with a semicolon (;). Preprocessor directives can be defined in source code or in the common line as argument during compilation.
Examples for preprocessing directives that can be used in C# include:
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Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.
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