option

The minimum warning level you want displayed for the build. Valid values are 0-4:

Warning level	Meaning
0	Turns off emission of all warning messages; display errors only.
1	Displays errors and severe warning messages.
2	Displays all errors and level 1 warnings plus certain, less-severe warnings, such as warnings about hiding class members.
3	Displays errors, level 1 and 2 warnings, plus certain, less-severe warnings, such as warnings about expressions that always evaluate to true or false.
4	Displays all errors, level 1-3 warnings, plus informational warnings. This is the default warning level at the command line.

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

Use /warnaserror to treat all warnings as errors up to the warning level specified. Higher-level warnings are ignored.

The compiler always displays errors.

/w is the short form of /warn.

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