Defining Macros with Parameters

1
Defining Macros with Parameters

• Defining constant macro
• define macro_name value
• For example
• define KMS_PER_MILE 1.609
• Defining macro with parameters
• define macro_name(parameter lis) macro body
• For example
• define SQUARE(n) ((n) (n))

2
Program Using a Macro with Parameters

• / Shows the definition and use of a macro /
• include ltstdio.hgt
• define LABEL_PRINT_INT(label, num) \
• printf("s d",
  (label), (num))
• int
• main(void)
• int r 5, t 12
• LABEL_PRINT_INT("rabbit", r)
• printf(" ")
• LABEL_PRINT_INT("tiger", t 2)
• printf("\n")
• return(0)
• rabbit 5 tiger 14

3
Macro Expansion

• LABEL_PRINT_INT(tiger, t2) Second macro
  call in the main
• LABEL_PRINT_INT(label, num)
• Parameter matching tiger t2
• printf(s d, (label), (num))
• parameter replacement in body
• printf(s d, (tiger), (t2))

4
Rules for Defining Macros with parameters

• Same as constant macro there is no at the end
  of macro definition
• To extend a macro over multiple lines, all except
  for the last line must end with backslash
  character /
• Operators with side effect should not be used as
  macro arguments.
• For example define RT(a) is wrong

5
Rules for Defining Macros with parameters

• Using the parenthesis for the formal parameters
  in Macro body is required to avoid the effect of
  operator precedence in macro expansion. For
  example
• Version 1 Version 2
• define SQUARE(n) n n define SQUARE(n)
  ((n) (n))
• SQUARE(x y)
  SQUARE(x y)
• becomes becomes
• x y x y ((x
  y) (x y))
• Problem multiplication done before addition
  in version 1, also.
• SQUARE(m) / SQUARE(n) SQUARE(m) /
  SQUARE(n)
• becomes becomes
• m m / n n ((m)
  (m)) / ((n) (n))
• Therefore, the result produced by version 1 is
  wrong

6
More examples of Macro with Parameters

• define ROOT1(a, b, c) \
• ((-(b) sqrt((b) (b) 4 (a) (c))) / (2
  (a)))
• Can be used in the main as
• r ROOT1(n1, n2, n3)
• define INDEXED-FOR(ct, st, end) \
• for ((ct) (st) (ct) lt (end) (ct))
• Can be used in the main as
• INDEXED_FOR(i,0,X_MAX)
• printf(x2d 6.2f\n, i, xi)