You can set directives that affect all files in a project during compilation.
The Compiler uses all directives specified in the project's properties when a project compiles, apart from those overridden by properties for individual files that differ from the project ones. To set Compiler directives in the project's properties:
The Compiler directives are saved with the project, so that they are used on all files in the project the next time you build the project.
These directives are overridden by directives specified for individual source files and for the build type.