program to remove comments from source

**Abda92** · 12-24-2006

Hi Iv been working on a program that opens a source file then copy's the src to another file excluding all comments. I have the idea and the concept, and have written this src:

Code:

#include <stdio.h>
#define IN 1       /* getc() is now reading comment(not outputting text) */
#define OUT 0      /* getc() isn't reading comment(outputting text) */

int main() {
   int mode, l, j, k;
   FILE *src, *newSrc;
   
   src = fopen("C:\\1-23.c", "rt");
   newSrc = fopen("C:\\src.c", "wt");
   mode = OUT;
   for (;;) {
      /* Entering comment */
      if ((l = getc(src)) == EOF) {
         printf("l End of file reached");
         break;
      }
      if ((j = getc(src)) == EOF) {
         printf("j End of file reached");
         break;
      }
      if (mode == OUT && l == '/' && j == '*') {
         mode = IN;
      }
      else if (mode == OUT && j == '/') {
         k = getc(src);
         if (k == '*') {
            mode = IN;
         }
         else {
            putc(j, newSrc);
            putc(l, newSrc);
            putc(k, newSrc);
            break;
         }
      }
      else if (mode == OUT) {
         putc(l, newSrc);
         putc(k, newSrc);
      }   
      /* Leaving comment */
      if (mode == IN && l == '*' && j == '/') {
         mode = OUT;
      }
      if (mode == IN && j == '/') {
         k = getc(src);
         if (k == '/') {
            mode = OUT;
         }
      }
   }
   fclose(src);
   fclose(newSrc);
   getchar();
   return 0;
}

I'm sorry if there's anything hard to understand in the source because i didn't write any comments. When i run this, it creates a blank file with weird characters in it. Can anyone please find were this bug is?

**vart** · 12-24-2006

Code:

 else {
            putc(j, newSrc);
            putc(l, newSrc);
            putc(k, newSrc);
            break;
         }

Wrong order of chars
No need to break...

There are other problems also...

**Happy_Reaper** · 12-24-2006

Why don't you work by getting one character at a time instead of 2 ? It would make a lot of thins simpler, if you ask me.

**Meshal** · 12-24-2006

another thing use fgetc instead of getc
http://www.cplusplus.com/ref/cstdio/fgetc.html

**Salem** · 12-24-2006

> #define IN 1
If you define more states, like COMMENT_LEADIN and COMMENT_LEADOUT then you only need to read one character at a time, and look at the current state to decide what the new state should be.

**Abda92** · 12-24-2006

thanks everyone i got it working with the following src:

Code:

#include <stdio.h>
#define IN 1       /* getc() is now reading comment(not outputting text) */
#define OUT 0      /* getc() isn't reading comment(outputting text) */

int main() {
   int mode, i, l, j, k;
   FILE *src, *newSrc;
   
   src = fopen("C:\\1-23.c", "rt");
   newSrc = fopen("C:\\src.c", "wt");
   mode = OUT;
   for (i = 1;;i++) {
      /* Entering comment */
      if ((l = getc(src)) == EOF) {
         printf("End of file reached");
         break;
      }
      if (mode == OUT && l == '/') {
         if ((j = getc(src)) == EOF) {
            printf("End of file reached");
         }
         else if (j == '*') {
            mode = IN;
         }
      }
      /* code to be written into new file if not entering comment */
      else if (mode == OUT) {
         putc(l, newSrc);
      }   
      /* Leaving comment */
      if (mode == IN && l == '*') {
         if ((j = getc(src)) == '/') {
            mode = OUT;
         }
      }
   }
   fclose(src);
   fclose(newSrc);
   getchar();
   return 0;
}

just a few questions for the future:

Originally Posted by meshal

another thing use fgetc instead of getc
http://www.cplusplus.com/ref/cstdio/fgetc.html

Can you please explain why? i checked the link you provided but i don't see a difference between the two functions.

Originally Posted by salem

> #define IN 1
If you define more states, like COMMENT_LEADIN and COMMENT_LEADOUT then you only need to read one character at a time, and look at the current state to decide what the new state should be.

can you please explain? i don't really understand.
Thanks again everyone i really appreciate your help.

**vart** · 12-24-2006

You can make 4 states
Out -> Comment_LEADIN -> IN -> Commen_LEADOUT -> OUT

The decision can be made based on one char only

**Cactus_Hugger** · 12-24-2006

thanks everyone i got it working with the following src:

Are you sure about that? This input:

Code:

#include <stdio.h>

int main()
{
	int x = 6 / 2;
	// This is a test
	/* This is a test */
	printf("/* Hey! Not really a test!*/\n");

	return 0;
}

Resulted in this output:

Code:

#include <stdio.h>

int main()
{
	int x = 6 2;
	 This is a test
	
	printf("\n");

	return 0;
}

Didn't accout for string literals (albeit that was a cruel test) but it trips over division.

Also, AFAIK, "wt" and "rt" are not valid modes for fopen(). (Perhaps "w+" and "r+"?) See the man page on fopen().

Also... why? Comments are a good thing, most of the time. (The fourth part of my signature is meant tongue in cheek, I assure you.

)

**Abda92** · 12-25-2006

Originally Posted by vart

You can make 4 states
Out -> Comment_LEADIN -> IN -> Commen_LEADOUT -> OUT

The decision can be made based on one char only

I'm sorry I still don't understand.

Originally Posted by Cactus_Hugger

Didn't accout for string literals (albeit that was a cruel test) but it trips over division.

Also, AFAIK, "wt" and "rt" are not valid modes for fopen(). (Perhaps "w+" and "r+"?) See the man page on fopen().

I'm sorry i wasn't clear enough, it only deletes C comments (/* */) not C++ comments ( // ). Although C compilers now support them. And "rt" and "wt" are valid modes for fopen(), the 't' is for "text". I know it's not needed but I write it to make it clear that it's a text file.

**vart** · 12-25-2006

I mean you can implement somethink like the following statechange algorithm base only on one character just read:

state = OUT:
if char == '/' -> state = LEADIN
else state = OUT

state = LEADIN:
if char == '*' -> state = IN
else if char == '/' state = LEADIN
else state = OUT;

state = IN:
if char == '*' -> state = LEADOUT
else state = IN

state = LEADOUT:
if char == '/' state = OUT
else if char == '*' -> state = LEADOUT
else state = IN

**Salem** · 12-25-2006

Like

Code:

enum state {
  s_code,
  s_commentleadin,
  s_comment,
  s_commentleadout,
  s_string,
  s_escaped
};

state s = s_code;
while ( (c=fgetc(fp)) != EOF ) {
  switch ( s ) {
    case s_code:
      if ( c == '/' ) state = s_commentleadin;
      else fput( out, c );
      break;
    case s_commentleadin:
      if ( c == '*' ) state = s_comment;
      else { fputc(out,'/'; fputc(out,c); state = s_code; }
      break;
  }
}

Read about finite state machines
http://en.wikipedia.org/wiki/Finite_state_machine

**Abda92** · 12-25-2006

Thanks alot. now I understand. I might change it or just keep it as is. Are there any advantages of using this method?

**Happy_Reaper** · 12-25-2006

I don`t see any immediate ones...

Thread: program to remove comments from source

Thread Tools

Search Thread

Display

program to remove comments from source

Similar Threads

How to make a program that prints it's own source code???

Totally confused on assigment using linked lists

comments my program

Multiple source files for one program