Page History

...

#define CUBE(I) ( (I) * (I) * (I) )
int a = 81 / CUBE(2 + 1);

Exceptions

PRE01-EX1: When the parameter names are surrounded by commas in the replacement text, regardless of how complicated the actual arguments are, there is no need for parenthesizing the macro parameters. Because commas have lower precedence than any other operator, there is no chance of the actual arguments being parsed in a surprising way.

#define FOO(a, b, c) bar(a, b, c)
/* ... */
FOO(arg1, arg2, arg3);

When token pasting, stringization, and string concatenation are desired, the arguments must not be parenthesized individuallyPRE01-EX2: Macro parameters cannot be individually parenthesized when concatenating tokens using the ## operator, converting macro parameters to strings using the # operator, or concatenating adjacent string literals. The JOIN() macro below concatenates both arguments to form a new token. The SHOW() macro converts the single argument into a string literal, which is then concatenated with the adjacent string literal to form the format specification in the call to printf().

#define JOIN(a, b) (a ## b)
#define SHOW(a) printf(#a " = %d\n", a) 

See PRE05-A. Understand macro replacement for more information on using the ## operator to concatenate tokens.

Risk Assessment

Failing to parenthesize the parameter names in a macro can result in unintended program behavior.

...