What is # operator or stringizing operator ?

The #operator is called stringizing operator. It allows a formal argument within a macro definition to be converted to a string. If a formal argument in a macro definition is preceded by this operator, the corresponding actual argument will automatically be enclosed in double quotes.

Consecutive whitespace characters inside the actual argument will be replaced by a single blank space, and any special characters, such as ‘ , “ and \, will be replaced by their corresponding escape sequences; e.g., \ ‘ , \ “ and \ \. In addition, the resulting string will automatically be concatenated (i.e., combined) with any adjacent strings.

Ex:

#include<stdio.h>

#define sum(xy) printf(#xy “=%d\n”,xy)

void main()

{

                ……………………

                ………………………

                sum(a+b);

                ……………………

                ………………….

}

Here printf(#xy “=%d\n”,xy) is equal to the printf(“a+b =%d\n”,a+b);