1.Difference between a macro and a function is that a macro returns code and a function returns a value.
2. macro 'calls' nearly always get expanded once at compile time wheras most function calls are evaluated many many times.
When you call a function your compiler enters a call-sequence (which takes
time) and allocates a new stack frame for that function (whcih takes text
stack space) so that the function's body can be executed. After it's done
you enter a returning-sequence phase (which takes time).
A macro does not need anything of the above, because it's preprocessor's job
to expand a macro, it's only about text replacement, not about compiler
stuff or code-generating issues. So you don't expend time and space doing
what a function would need in order to be executed.
That makes functions and macros[/b] completely different even if the result of
using both is, in some cases, the same. One must know it's suitable to use
one or the other. For instance: you can't point a pointer to a macro, but
you can use pointers to functions...
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