warn-compiler-option.md

title	-warn (C# Compiler Options)
ms.date	07/20/2015
ms.prod	.net
ms.technology	devlang-csharp
ms.topic	article
f1_keywords	/warn
helpviewer_keywords	warning level [C#] /w compiler option [C#] -w compiler option [C#] -warn compiler option [C#] /warn compiler option [C#] w compiler option [C#] warn compiler option [C#]
ms.assetid	5f80ff59-4991-4382-9f9a-77da18446e71
caps.latest.revision	17
author	BillWagner
ms.author	wiwagn

-warn (C# Compiler Options)

The -warn option specifies the warning level for the compiler to display.

Syntax

-warn:option  

Arguments

option
The warning level you want displayed for the compilation: Lower numbers show only high severity warnings; higher numbers show more warnings. Valid values are 0-4:

Warning level	Meaning
0	Turns off emission of all warning messages.
1	Displays severe warning messages.
2	Displays level 1 warnings plus certain, less-severe warnings, such as warnings about hiding class members.
3	Displays level 2 warnings plus certain, less-severe warnings, such as warnings about expressions that always evaluate to true or false.
4 (the default)	Displays all level 3 warnings plus informational warnings.

Remarks

To get information about an error or warning, you can look up the error code in the Help Index. For other ways to get information about an error or warning, see C# Compiler Errors.

Use -warnaserror to treat all warnings as errors. Use -nowarn to disable certain warnings.

-w is the short form of -warn.

To set this compiler option in the Visual Studio development environment

1. Open the project's Properties page.

2. Click the Build property page.

3. Modify the Warning Level property.

For information on how to set this compiler option programmatically, see xref:VSLangProj80.CSharpProjectConfigurationProperties3.WarningLevel%2A.

Example

Compile in.cs and have the compiler only display level 1 warnings:

csc -warn:1 in.cs  

See Also

C# Compiler Options
Managing Project and Solution Properties