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#line lets you modify the compiler's line number and (optionally) the file name output for errors and warnings.

#line [ number ["file_name"] | hidden | default ]


The number you want to specify for the following line in a source code file.
"file_name" (optional)
The file name you want to appear in the compiler output. By default, the actual name of the source code file is used. The file name must be in double quotation marks ("").
Hides the successive lines from the debugger until another #line directive is encountered.
Resets the line numbering in a file.


The #line directive might be used in an automated, intermediate step in the build process. For example, if lines were removed from the original source code file, but you still wanted the compiler to generate output based on the original line numbering in the file, you could remove lines and then simulate the original line numbering with #line.

The #line hidden directive hides the successive lines from the debugger, such that when the developer steps through the code, any lines between a #line hidden and the next #line directive (assuming that it is not another #line hidden directive) will be stepped over. This option can also be used to allow ASP.NET to differentiate between user-defined and machine-generated code. Although ASP.NET is the primary consumer of this feature, it is likely that more source generators will make use of it.

A #line hidden directive does not affect file names or line numbers in error reporting. That is, if an error is encountered in a hidden block, the compiler will report the current file name and line number of the error.

A source code file can have any number of #line directives.

Example 1

The following example shows how to report two warnings, associated with line numbers. The #line 200 directive forced the line number to be 200 (although the default is #7). The other line (#9) follows the usual sequence as a result of the default #line directive.

// preprocessor_line.cs
public class MyClass2
   public static void Main() 
      #line 200
      int i;   // CS0168 on line 200
      #line default
      char c;   // CS0168 on line 9

Example 2

The following example shows how the debugger ignores the hidden lines in the code. When you run the example, it will display three lines of text. However, when you set a break point, as shown in the example, and hit F10 to step through the code, you will notice that the debugger ignores the hidden line. Notice also that even if you set a break point at the hidden line, the debugger will still ignore it.

// preprocessor_linehidden.cs

using System;

class MyClass 
   public static void Main() 
      Console.WriteLine("Normal line #1.");   // Set a break point here.
      #line hidden
      Console.WriteLine("Hidden line.");
      #line default
      Console.WriteLine("Normal line #2.");

See Also

C# Preprocessor Directives