This option removes any initial definition of the macro name.
The macro name can be either:
Note
Not all compiler predefined macros can be undefined.
-Uname
Where:
nameis the name of the macro to be undefined.
Specifying -Uname has the same effect as placing the text #undef name at the head of each source file.
The compiler defines and undefines macros in the following order:
compiler predefined macros
macros defined explicitly, using ‑Dname
macros explicitly undefined, using ‑Uname.