Do I need to #undef a local #define? Is there such a thing as a local define?

Question

Sometimes to make things easier to write and read, I write some local #define macros within functions (for example, #define O_REAL Ogre::Real).

Answer 1

#define is handled by the preprocessor, which doesn't actually know C syntax at all. A #define ignores scope, and will remain in effect until you #undef it or until the end of the compilation unit.