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/Wn, /WX, /Wall, /wnn, /wdn, /wen, /won (Warning Level)

/Wn
/WX
/Wall
/wnn
/wdn
/wen
/won

These options specify how the compiler generates warnings for a given compilation.

Option  
/Wn Specifies the highest level of warning generated by the compiler. Valid warning levels for n range from 0 to 4:
  • Level 0 disables all warnings.
  • Level 1 displays severe warnings.
  • Level 2 displays all level 1 warnings and warnings less severe than level 1. Level 2 is the default warning level at the command line.
  • Level 3 displays all level 2 warnings and all other warnings recommended for production purposes.
  • Level 4 displays all level 3 warnings plus informational warnings, which in most cases can be safely ignored. This option should be used only to provide "lint" level warnings and is not recommended as your usual warning level setting.

For a new project, it may be best to use /W4 in all compilations. This will ensure the fewest possible hard-to-find code defects.

/Wall Enables all warnings, including those disabled by default. See Compiler Warnings That Are Off By Default.
/WX Treats all warnings as errors. For a new project, it may be best to use /WX in all compilations; resolving all warnings will ensure the fewest possible hard-to-find code defects.
/wnn Specifies the level for a particular warning. The first parameter sets the warning level (same as /Wn) and the second parameter is the actual warning number.

For example, /w14326 causes C4326 to be generated as a level 1 warning.

/wdn Disables the specified compiler warning where n is the compiler warning number.

For example, /wd4326 disables compiler warning C4326.

/wen Treats the specific compiler warning as an error where n is a compiler warning.

For example, /we4326 flags warning number C4326 as an error.

/won Reports the error only once where n is a compiler warning.

For example, /wo4326 will cause warning C4326 to be reported only once.

If you create a precompiled header (/Yc) with one of the /w options, any use of the precompiled header (/Yu) will cause those same /w options to be in effect again. You can override the /w setting in the precompiled header with another /w option at the command line.

Pragma directives in source code are unaffected by the /w option.

You can also use #pragma warning to control the level of warning reported at compile time.

The Build Errors documentation describes the warnings, indicates each warning's level, and indicates potential problems (rather than actual coding errors) with statements that may not compile as you intend.

To set this compiler option in the Visual Studio development environment

  1. Open the project's Property Pages dialog box. For details, see Setting Visual C++ Project Properties.
  2. Click the C/C++ folder.
  3. Click the General property page and modify the Warning Level or Treat Warnings as Errors properties.
  4. Click the Advanced property page and modify the Disable Specific Warnings property.
  5. For the remaining options, click the Command Line property page and type the compiler option in the Additional Options box.

To set this compiler option programmatically

See WarningLevel Property, WarnAsError Property, DisableSpecificWarnings Property, and AdditionalOptions.

See Also

Compiler Options | Setting Compiler Options

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