## operator in c language

madhuri thalluri

Hello friends,
can anyone explain about the ##operator in c language and how it works??

I think you couldn't find any documentation regarding this as it is very poorly documented and hence you had to post a question on that.
Actually, ## is called the token pasting operator and concatenates the characters defined around it (excluding the white spaces). It is generally used in your definition macro.
ex:

#define my_name v ##       i ##s        ##hal

the above statement will define my_name as vishal, hope you understood what happened above.

## can also be used to do beautiful things like executing your code without actually typing "main" anywhere in the code. However, Internally ## creates a string main. Take a look at this example, try copying it in an editor and run it See what happens

#define vishal(s,t,u,m,p,e,d) m##s##u##t
#define freak vishal(a,n,i,m,a,t,e)
#include<stdio.h>

int freak() {
    printf("hello world");
    getchar();
    return 0;
}

In the above code we define a function vishal with 7 parameters s,t,u,m,p,e,d whose task is to concatenate the parameters m,s,u,t. Now, in the second macro definition, we are calling the function vishal() as vishal(a,n,i,m,a,t,e), whose result is stored in a variable freak. When this executes, It concatenates the parameters m,s,u,t which are m,a,i,n in the calling function (line 2). So, freak now holds the string "main"
And hence the code executes perfectly.

Hope, I was clear.