program to remove comments from source

This is a discussion on program to remove comments from source within the C Programming forums, part of the General Programming Boards category; Hi Iv been working on a program that opens a source file then copy's the src to another file excluding ...

  1. #1
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    program to remove comments from source

    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?

  2. #2
    CSharpener vart's Avatar
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    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...
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  3. #3
    Fear the Reaper...
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    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.
    Teacher: "You connect with Internet Explorer, but what is your browser? You know, Yahoo, Webcrawler...?" It's great to see the educational system moving in the right direction

  4. #4
    C 1337 Meshal's Avatar
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    another thing use fgetc instead of getc
    http://www.cplusplus.com/ref/cstdio/fgetc.html

  5. #5
    and the hat of wrongness Salem's Avatar
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    > #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.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  6. #6
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    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:
    Quote 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.
    Quote 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.

  7. #7
    CSharpener vart's Avatar
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    You can make 4 states
    Out -> Comment_LEADIN -> IN -> Commen_LEADOUT -> OUT

    The decision can be made based on one char only
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  8. #8
    int x = *((int *) NULL); Cactus_Hugger's Avatar
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    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. )
    long time; /* know C? */
    Unprecedented performance: Nothing ever ran this slow before.
    Any sufficiently advanced bug is indistinguishable from a feature.
    Real Programmers confuse Halloween and Christmas, because dec 25 == oct 31.
    The best way to accelerate an IBM is at 9.8 m/s/s.
    recursion (re - cur' - zhun) n. 1. (see recursion)

  9. #9
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    Quote 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.
    Quote 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.

  10. #10
    CSharpener vart's Avatar
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    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
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  11. #11
    and the hat of wrongness Salem's Avatar
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    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
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  12. #12
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    Thanks alot. now I understand. I might change it or just keep it as is. Are there any advantages of using this method?

  13. #13
    Fear the Reaper...
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    I don`t see any immediate ones...
    Teacher: "You connect with Internet Explorer, but what is your browser? You know, Yahoo, Webcrawler...?" It's great to see the educational system moving in the right direction

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