This option removes any initial definition of the macro name
The macro name
a predefined macro
a macro specified using the
-Doption.
Note
Not all compiler predefined macros can be undefined.
SyntaxSpecifying -U has
the same effect as placing the text name#undef at
the head of each source file.name
The compiler defines and undefines macros in the following order:
compiler predefined macros
macros defined explicitly, using
-Dnamemacros explicitly undefined, using
-U.name
PDF version