宏作为C中宏的参数

Question

I want to know which macro gets replaced first in the following code

#define A 100
#define B 200
#define C(A,B) A+B

here when we use C, then evaluation will be from left to right or right to left. That is B gets the value first or A gets the value first

i gave this example just to make things look simple, may be i was wrong. the actual thing i want to ask is, if A and B also take arguments and have the scope of expansion, then which one would expand first

Answer 1

I'm not sure what you mean. There's never a point where you can "see" half a result of the preprocessor; the entire input file is preprocessed, then handed over to the compiler.

I think that the names for the macro arguments will never also be replaced as if they were stand-alone symbols.

I tried it, and this program:

#include <stdio.h>

#define A 100
#define B 200
#define C(A, B) A + B

int main(void) {
  printf("A=%d\nB=%d\nC(1,2)=%d\n", A, B, C(1,2));
  return 0;
}

prints

A=100
B=200
C(1,2)=3

So, C(1,2) expands to 1 + 2 , the definitions of A and B don't matter.

Of course I must say that I find the above very bad practice , since it's quite confusing. Never use all-caps names for macro arguments, since macros and preprocessor symbols tend to use such names.