Why pre-processor gives a space in comments?

[KAILEY]

Hello friends,
I want to write program in c++ language in which I want to comment a line using the pre-processor in the following ways.

#define open 
#define close
main()
{
        // your code 
}

In my code when I used $gcc -E filename.c I expected

/* commented line */

but I got

/ * commented line */

I don't know why pre-processor gives a space in comments? Please help me to fix this problem.

[Katty]

As per my information pre-processor is used to runs and produces the source code into the machine language code that is understand by C compiler. Pre-processor processes your code only once and for this reason even if you create "/*" using your #define then C compiler would see the "/*" in your code and will give an error message, because it is an invalid code rather it is preprocessing instruction.

[kelfro]

I think "#define" is the only preprocessing instruction you have used in your code. As per my information "/*" is not a preprocessor instruction, rather it is used to define comments. The main work of preprocessor is that, it used to remove comments before passing the source code to the c- compiler. I think comments are used as whitespace and not an preprocessing tokens.

[Zecho]

As per GNU C Preprocessor documentation 2 tokens which used one valid token can not be pasted together. It means that you can not concatenate "y" with "+" in either order. If you accidentally tried this then you will get an error message. It unnecessarily put concatenate x with + in either order. It also use '##' in complex macros unnecessarily. If you get an error message then you have to remove '##' from your code to fix this problem.

[absolute55]

You get an error because "/*" is not a valid token. As per my information 2 tokens which are not form valid token cannot be pasted together. As per my information "##" is unnecessarily used to avoid creating a comment and avoid confusion. To fix this problem Avoid comment headers because they already used in stage 3. To fix this problem you have to use following code:

if ((*plhss)->types == CPPs_DIVs && rhss->types != CPPs_EQs)
        *ends++ = ' ';

[Reegan]

If you want to comment your source code using pre-processor then you have to use following code:

#if 0
...
#endif

This is used to replace comments with spaces before preprocessor runs. If you put / and * characters together, then you will get /* which is called as couple operators.