Exercise 1-23

Exercise 1-23  Write a program to remove all comments from a C program.  Don't forget to handle quoted strings and character constants properly.  C comments do not nest.

I used function pointers for this, which may not be the best solution.

#include <stdio.h>

  /* Function prototypes. */

void normal(char c);

void backslash(char c);

void open_slash(char c);

void in_comment(char c);

void close_asterisk(char c);

void in_double_quotes(char c);

void in_single_quotes(char c);

void backslash_double(char c);

void backslash_single(char c);

  /* Our function pointer. */

void (*state)(char c);

void normal(char c)

{

  if (c=='/')

    state = open_slash;

  else

  {

    if (c=='\'')

      state = in_single_quotes;

    else if (c=='\"')

      state = in_double_quotes;

    putchar(c);

  }

}

void backslash_double(char c)

{

  /* Ignore the next character. */

  state = in_double_quotes;

}

void backslash_single(char c)

{

  /* Ignore the next character. */

  state = in_single_quotes;\

}

void open_slash(char c)

{

  if (c=='*')

    state = in_comment;

  else if (c=='/')

    putchar('/');

  else

  {

    putchar('/');

    putchar(c);

    state = normal;

  }

}

void in_comment(char c)

{

  if (c=='*')

    state = close_asterisk;

}

void close_asterisk(char c)

{

  if (c=='/')

    state = normal;

  else if (c!='*')

    state = in_comment;

  /* else state = close_asterisk; */

}

void in_double_quotes(char c)

{

  if (c=='"')

    state = normal;

  if (c=='\\')

    state = backslash_double;

  putchar(c);

}

void in_single_quotes(char c)

{

  if (c=='\'')

    state = normal;

  if (c=='\\')

    state = backslash_single;

  putchar(c);

}

int main(void)

{

  int c;

  state = normal;

  while (c = getchar(), c!=EOF)

    (*state)(c);

  /* We could warn the user about an unclosed comment,

   * or single or double quotes. */

  return 0;

}