Scope rules for C macros

Question

I'm not much of a C programmer, but I was under the assumption that C macros were almost sort of a find and replace feature where the pre-processor takes the macro definition and puts it wherever it sees the macro name.

This is the Dragon Book's example of dynamic scope rules and how they apply to macros:

#define a (x + 1)

int x = 2;
void b () { int x = 1; printf("%d\n", a); }
void c () { printf("%d\n", a); }
void main () { b(); c(); }

They also discuss how dynamic scope rules apply to the name x within macro a. I was under the assumption that it would basically replace a with (x + 1) and then compile the program and so the scope rules would be exactly the same as if you had written (x + 1) instead of a (which would be static scope rules).

Could anyone clarify this?

Edit: Book referred to is Compilers: Principles, Techniques & Tools Second Edition. The example quoted is from pages 31-32.

Answer 1

Your understanding is correct: find every use of the identifier a and substitute that a with (x + 1). That is exactly what the preprocessor does.

The only "scope" that we can discuss with respect to an object-like macro (like a) is the scope of the macro itself: The scope of a macro is from the line on which it is defined (with a #define directive) until the line on which it is undefined (with a #undef directive) or until the end of the translation unit (the .cpp and all of the headers it includes), if it is never undefined.