Thread: Help with writing a preprocessor to remove comments

Hi,

I have an assignment for homework which is giving me trouble. You can see by the code I have started I am just stuck. Also this code (bad as it is) is 100% mine no copying pasting etc... The assisnment is such that we have to write a program to remove comments and replace them with a space. A comment in our case is considered to start with /* and end with */ so if you had /*abc*/ abc would be replaced with a space. It needs to operate with standard Input Output streams. So the programs name is decomment and the execution would look something like this
decomment < somefile.c > somefilewithoutcomments.c 2> errorandwarningmessages

I'm a bit lost but more then willing to put the work in to get it right. Any help is greatly appreciated. My code isn't to great it needs work, I'm not even sure what to return I know it needs to return success and non-success(errors) but not sure how to do that. But as I said I will work to make it better.

Code:

#include<stdio.h>



int main ()

     enum state {Out, Slash, In, Star;}
int c = getchar();

Switch (state)

{case Out:
 if c=='/'
 state = Slash
break;

case Slash:
if c =='*'
state = In

else if(c!='*')
state = Out
break;

case In:
if c=='*'
state = star
break;


      case Star:
if c == '/'
state = Out
else if (c!='*')
state = In

       }

So, you want to copy a c file without comments? Well, you have to actually write the file. Apart from obvious syntax errors, you need to plan to encounter both the characters individually where they are not comments. For example you might find division expressions or multiplication expressions. You need to store both the '/' and a '*' to find a comment. When you do, you output a space as required. When you find those in reverse order, you know where to start copying the file again.

Well if you are referring to the othe C file, the whose comments will be removed, there are many files I can choose from, there's not one in particular. In terms of the file to do the decommenting, that's what I need help with.

I'm referring to what your program should actually do.

Well yes, I guess I'm just not sure how. I have the switch statement and anything that's in the In state or Star State is a comment and should be replaced with a space. How to get it to do that and how to output errors like if someone starts a comment but never finishes is what I nees help in

Sure I know what to do from a big picture standpoint. Something like if case = Star || case = in
char = " " but exactly how to do it and apply it, I am not sure, I think I just need help getting started. Any help at all is greatly appreciated.

Hey Tater,

Sure let me take this one step at a time. How would I save the file to memory and treat it as a string. She wants it to be a character, so I don't think I can use that option.

Ok in plain English what I want to do is this. Write a program that takes another C program and anywhere in between /* and */ I want to replace with a space. Therefore it will be decommented. I want to also write to stderr, if for example a comment is started but not finished so /* without a */ later on in the text should return an error

Then, finally there's the little problem of nested comments which happen when a section of code containing comments is commented out..

Originally Posted by C89 Draft

3.1.9 Comments

Except within a character constant, a string literal, or a comment, the characters /* introduce a comment. The contents of a comment are examined only to identify multibyte characters and to find the characters */ that terminate it.21

21

Thus comments do not nest.

AFAICT, this has not changed since then.

Thanks Tater,

What you described seems like it may be more advanced then where we are at. I have no idea how to do that. Keep in mind our programs are very small right now. I don't know I'm confused about the whole thing.

Ok... I give up...

These last few days it seems like every darned thing I say just gets chewed up and spit back at me. Enjoy your forums, people... I've had all of this I'm going to take.

Bye!