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 1 is the default warning level at the command line.
Level 2 displays all level 1 warnings and warnings less severe than level 1.
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.