#warning lets you generate a level one warning from a specific location in your code.

#warning text

where:

text

The text of the warning that should appear in the compiler's output.

Remarks

A common use of #warning is in a conditional directive. It is also possible to generate a user-defined error with #error.

Example

// preprocessor_warning.cs
// CS1030 expected
#define DEBUG
public class MyClass 
{
   public static void Main() 
   {
      #if DEBUG
      #warning DEBUG is defined
      #endif
   }
}

See Also

C# Preprocessor Directives