练习 6-3 编写一个交叉引用程序，打印文档中所有单词的列表，并且每个单词还有一 个列表，记录出现过该单词的行号。对 the、and 等非实义单词不予考虑。

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


#define MAXWORD 100

/*Author Stat:  founded 2017 11 26*/
static int count_line = 1;


struct line{
   int line;
   struct line *next;
};


struct tnode{
   char *word;
   struct line *start;
   struct tnode *next;
};


struct tnode *addItem(struct tnode *,char *);
struct line *addlines(struct line *);
void showItem(struct tnode *);
void showLine(struct line *);
struct tnode *Ialloc(void);
struct line *Lalloc(void);
char *walloc(char *);
int getword(char *,int);
int Nonrealword(char *);


int main(void)
{
   struct tnode *head;
   char word[MAXWORD];


   head = NULL;
   while(getword(word,MAXWORD) != EOF)
      if(Nonrealword(word))
         if(isalpha(word[0]))
       head = addItem(head,word);
   printf("%33s\n\n","Words  Line Number");
   showItem(head);


   return 0;
}


struct tnode *addItem(struct tnode *p,char *w)
{
   if(p == NULL){
      if((p = Ialloc()) == NULL){
    printf("Out of memory!\n");
    exit(EXIT_FAILURE);
 }
      if((p->word = walloc(w)) == NULL){
    printf("Out of memory!\n");
    exit(EXIT_FAILURE);
 }
      if((p->start = Lalloc()) == NULL){
    printf("Out of memory!\n");
    exit(EXIT_FAILURE);
 }
      p->start->line = count_line;
      p->start->next = NULL;
      p->next = NULL;
   }else if(strcmp(p->word,w) == 0)
      p->start = addlines(p->start);
   else
      p->next = addItem(p->next,w);
   return p;
}


struct line *addlines(struct line *p)
{
   if(p == NULL){
     if((p = Lalloc()) == NULL){
    printf("Out of memory!\n");
    exit(EXIT_FAILURE);
}
     p->line = count_line;
     p->next = NULL;
   }else if(p->line == count_line)
     ;
   else
     p->next = addlines(p->next);
   return p;
}


void showItem(struct tnode *p)
{
   if(p != NULL){
     printf("%20s  ",p->word);
     showLine(p->start);
     printf("\n");
showItem(p->next);
free(p);
  }
}


void showLine(struct line *p)
{
   if(p != NULL){
     printf("%d ",p->line);
     showLine(p->next);
free(p);
   }
}


struct tnode *Ialloc(void)
{
   return (struct tnode *)malloc(sizeof(struct tnode));
}


struct line *Lalloc(void)
{
   return (struct line *)malloc(sizeof(struct line));
}


char *walloc(char *w)
{
   char *p;


   if((p = (char *)malloc(strlen(w)+1)) != NULL)
      strcpy(p,w);
   return p;
}
int getword(char *word,int max)
{
   int c,getch(void);
   void ungetch(int);
   char *w = word;


   while(isspace(c = getch()))
      if(c == '\n')
         count_line++;
   if( c != EOF)
      *w++ = c;
   if(!isalpha(c)){
      *w = '\0';
      return c;
   }
   for(;--max; w++)
      if(!isalnum(*w = getch()))
    break;
   if(*w != '\'')
      ungetch(*w);
   else{
      w++;
      for(;--max;w++)
      if(!isalnum(*w = getch())){
         ungetch(*w);
    break;
      }
   }
   *w = '\0';


   return word[0];
}


int Nonrealword(char *s)
{
   int i;
   static char *list[] = {
      "a","an","and","be","but","by","he","I","is","off","on",
      "she","so","the","they","you",NULL
   };


   i = 0;
   while(list[i]){
      if(strcmp(list[i],s) == 0)
    return 0;
      i++;
   }
   return 1;
}


#define BUFSIZE 100


static char buf[BUFSIZE];
static int ps = 0;


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


void ungetch(int c)
{
   if(ps > BUFSIZE)
      printf("stack too full!\n");
   else
      buf[ps++] = c;

}