Exercise 1.23 - Remove comments from a C program

Question

Write a program to remove all comments from a C program. Don’t forget to handle quoted strings and character constants properly. C comments don’t nest.

Solution

/* Program to remove comments from a C Program.
   Program should echo quotes and character constants properly
   C Comments do not nest */

#include<stdio.h>

void rcomment(int c);
void incomment(void);
void echo_quote(int c);

int main(void)
{
    int c,d;

    printf(" To Check /* Quoted String */ \n");

    while((c=getchar())!=EOF)
        rcomment(c);

    return 0;
}

void rcomment(int c)
{
    int d;
    if( c == '/')
    {
        if((d=getchar())=='*')
         incomment();
        else if( d == '/')
        {
            putchar(c);
            rcomment(d);
        }
        else 
        {
            putchar(c);
            putchar(d);
        }
    }
    else if( c == '\''|| c == '"')
        echo_quote(c);
    else
        putchar(c);
}

void incomment()
{
    int c,d;
     
    c = getchar();
    d = getchar();

    while(c!='*' || d !='/')
    {
        c =d;
        d = getchar();
    }
}

void echo_quote(int c)
{
    int d;

    putchar(c);
    
    while((d=getchar())!=c)
    {
        putchar(d);
        
        if(d = '\\')
            putchar(getchar());
    }
    putchar(d);
}
    
Run this

Explanation

If two subsequent characters start with / and *, we say we are in-comment, If we find two characters which are / and /, we will print the first character and start treating the second / as the possible start of comment. In the same manner, if we encouter a single quote or a double quote character, then we understand we are inside a quoted string, so we putchar everything before we find the matching character again. Within a quoted string, if we encouter a special character, then we try to read them literally as two characters and print them.

If / is followed by any other character, we simply print them.

Comments by Disqus