C macro
Definition
A macro is #define directive with multiple parameterized substitutions.
Syntax
The general form of the kind of substitution directive just discussed is the following:
#define macro_name( list_of_identifiers ) substitution_string Example 1
Replacement of the identifier by using a statement or expression.
#define CUBE(x) x*x*x/*from w w w . ja v a2 s .co m*/
#include <stdio.h>
main (){
int k = 5;
int j = 0;
j = CUBE(k);
printf ("value of j is %d\n", j);
}
The code above generates the following result.
Example 2
Macro just indicates replacement, not the function call.
#include <stdio.h>
//from w w w. j ava 2s. c o m
#define add(x1, y1) x1 + y1
#define mult(x1,y1) x1 * y1
main ()
{
int a,b,c,d,e;
a = 2;
b = 3;
c = 4;
d = 5;
e = mult(add(a, b), add(c, d));
// mult(a+b, c+d)
// a+b * c+d
printf ("The value of e is %d\n", e);
}
The code above generates the following result.
Example 3
Defining a macro to output the value of an expression
#include <stdio.h>
/*from w w w . j a v a2 s.co m*/
#define print_value(expr) printf("\n" #expr " = %lf", (double)expr);
void main() {
int n = 10;
double f = 6.5;
print_value( n );
print_value( f );
printf("\n");
print_value(f * f + 4.0);
print_value( n / 2 + 3);
print_value( 3 * 4 + 12 / 2 - 8);
printf("\n");
}