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What are C# pre-processor directives?
The preprocessor directives give instruction to the compiler to preprocess the information before actual compilation starts.
All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. Preprocessor directives are not statements, so they do not end with a semicolon (;).
The following are some of the preprocessor directives in C#.
| Sr.No | Preprocessor Directive & Description |
|---|---|
| 1 | #define It defines a sequence of characters, called symbol. |
| 2 | #undef It allows you to undefine a symbol. |
| 3 | #if It allows testing a symbol or symbols to see if they evaluate to true. |
| 4 | #else It allows to create a compound conditional directive, along with #if. |
| 5 | #elif It allows creating a compound conditional directive. |
| 6 | #endif Specifies the end of a conditional directive. |
| 7 | #line It lets you modify the compiler's line number and (optionally) the file name output for errors and warnings. |
| 8 | #error It allows generating an error from a specific location in your code. |
Let us see an example of the #define preprocessor that defines a sequence of characters.
Example
#define PI
using System;
namespace PreprocessorDAppl {
class Program {
static void Main(string[] args) {
#if (PI)
Console.WriteLine("PI is defined");
#else
Console.WriteLine("PI is not defined");
#endif
Console.ReadKey();
}
}
}Output
PI is defined
Updated on: 23-Jun-2020
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