> On Jul 25, 2015, at 11:03 AM, Quincey Morris > <[email protected]> wrote: > > On Jul 25, 2015, at 10:37 , Carl Hoefs <[email protected] > <mailto:[email protected]>> wrote: >> >> Effectively, what the compiler does with a #define _is_ a global replace. > > It’s not, though. Not in general. > > 1. It’s not global. A #define can be undefined and redefined. > > 2. It’s not unique. IIRC, the appearance of the define symbol inside its own > definition is *not* subject to macro expansion. > > 3. Macro expansion happens as a separate lexical pass over the input. For > example, if source lines are not compiled as a result of a define/if then > it’s not clear what replacement might be suitable at refactoring. Or again, > token pasting may simply produce incorrect results if macro names are > arbitrarily changed around them.
Yes, your point 3 is primarily what I hadn't considered. -Carl
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