Cited from BTP300 Chris seneca cs Web
- Continuation
A macro definition may extend over several lines. The backslash character - \ - immediately followed by the end-of-line character identifies a continuation onto the next line. For example,
#define PI 3.141\
592654
is the same as
#define PI 3.141592654
Efficiency and Flexibility
Function-like macros provide efficient and flexible solutions. They avoid the overhead of function calls and do not impose type constraints on the parameters in the macro definition.
#define SQUARE(x) ((x) * (x)) /* NOTE THE PARENTHESES *// Fardad noted in class
Side-Effects
Macro definitions can also generate side effects. Because the pre-processor substitutes textual patterns rather than values, it can generate repeated evaluations of expressions that were intended to be a single evaluation. Such as area(r++).
#define PI 3.14
#undef PI
#define PI 3.14159 /* OK */
#define AREA(r) PI * r * r- Predeined macros
printf("The name of the source file is %s\n", __FILE__);
printf("The date of its translation is %s\n", __DATE__);
printf("The time of its translation is %s\n", __TIME__);
if (__STDC__ != 0)
printf("Compiled under Standard C\n");
else
printf("Not compiled under Standard C\n");
