Exercise 6.1 - getword

Question

Our version of getword does not properly handle underscores, string constants, comments, or preprocessor control lines. Write a better version.

#include <stdio.h>
#include <ctype.h>
#include <string.h>

struct key {
    char *word;
    int count;
} keytab[] = {
    "auto", 0,
    "break", 0,
    "case", 0,
    "char", 0,
    "const", 0,
    "continue", 0,
    "default", 0,
    "do", 0,
    "double", 0,
    "else", 0,
    "enum", 0,
    "extern", 0,
    "float", 0,
    "for", 0,
    "goto", 0,
    "if", 0,
    "int", 0,
    "long", 0,
    "register", 0,
    "return", 0,
    "short", 0,
    "signed", 0,
    "sizeof", 0,
    "static", 0,
    "struct", 0,
    "switch", 0,
    "typedef", 0,
    "union", 0,
    "unsigned", 0,
    "void", 0,
    "volatite", 0,
    "while", 0
};

int mygetword(char *, int);
int binsearch(char *, struct key*, int);

#define NKEYS (sizeof(keytab)/sizeof(keytab[0]))
#define MAXWORD 100

int main(int argc, char *argv[])
{   
    int n;
    char word[MAXWORD];

    while (mygetword(word, MAXWORD) != EOF)
       if (isalpha(word[0]))
            if ((n = binsearch(word, keytab, NKEYS)) >= 0)
                keytab[n].count++;
    for (n = 0; n < NKEYS; n++)
        if (keytab[n].count > 0)
            printf("%4d %s\n",
                keytab[n].count, keytab[n].word);
}

int binsearch(char *word, struct key keytab[], int n)
{
    int cond;
    int low, high, mid;

    low = 0;
    high = n -1;
    while (low <= high) {
        mid = (low+high) /2;
        if ((cond = strcmp(word, keytab[mid].word)) < 0 )
            high = mid - 1;
        else if (cond > 0)
            low = mid + 1;
        else
            return mid;
    }
    return -1;
}

int mygetword(char *word, int lim)
{
    int c, getch(void);
    void ungetch(int);
    char *w = word;
    int t;

    while (isspace(c=getch()))
        ;
    if (c != EOF)
        *w++ = c;
    if (!isalpha(c)) {
        if (c == '\"') { /*string constant*/
            for(c=getch(); c!= '\"'; c=getch()) 
                ; 
        }
        else if (c == '#') { /*preprocessor*/
            for(c=getch(); c!= '\n'; c=getch()) 
                ;
        }
        else if (c == '/')  /*comment*/
            if ((c=getch()) == '/') { /*single comment*/
                for(c=getch(); c!= '\n'; c=getch()) 
                    ;
            }
            else if (c == '*') { /*mutiline comment*/
                for(c=getch(),t=getch(); c!= '*' && t!= '/'; c=getch(), t=getch()) 
                    ungetch(t);
            }
            else ungetch(c);
        else /*underscore*/
            for( ; !isspace(c) && c!=EOF; c=getch()) 
                ;
        if (c != '\"' && c!='\n' && c!='/') 
            ungetch(c);
        *w = '\0';
        return c;
    }
    
    for ( ; --lim > 0; w++)
        if (!isalnum(*w = getch())) {
            if (!isspace(*w)){
                ungetch(*w);
                return (*w);
            }
            else {
                ungetch(*w);
                break;
            }
        }
    *w = '\0';
    return word[0];
}

#define BUFSIZE 100
char buf[BUFSIZE];
int bufp = 0;

int getch(void)
{
    return (bufp>0) ? buf[--bufp] :getchar();
}

void ungetch(int c)
{
    if (bufp >= BUFSIZE)
        printf("ungetch: too many characters\n");
        else buf[bufp++] = c;
}
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