Inline functions vs Preprocessor macros

Question

How does an inline function differ from a preprocessor macro?

Answer 1

The Inline function are expanded by the compiler where as the macros are expanded by the Preprocessor, which is mere textual substitution.Hence

• There is no type checking during macro invocation while type checking is done during function call.

• Undesired results and inefficiency may occur during macro expansion due to reevaluation of arguments and order of operations. For example

  #define MAX(a,b) ((a)>(b) ? (a) : (b))
  int i = 5, j = MAX(i++, 0);
  

  would result in

  int i = 5, j = ((i++)>(0) ? (i++) : (0));
  

• The macro arguments are not evaluated before macro expansion

  #define MUL(a, b) a*b
  int main()
  {
    // The macro is expended as 2 + 3 * 3 + 5, not as 5*8
    printf("%d", MUL(2+3, 3+5));
   return 0;
  }
  // Output: 16`
  

• The return keyword cannot be used in macros to return values as in the case of functions.

• Inline functions can be overloaded

• The tokens passed to macros can be concatenated using operator ## called Token-Pasting operator .

• Macros are generally used for code reuse where as inline functions are used to eliminate the time overhead (excess time) during function call(avoiding a jump to a subroutine).