初步剖析C语言编程中的结构体

#include 
#include 
#include 
#include"tNode.h" 
 
#define MAXWORD 100 
struct tnode *addtree(struct tnode *,char *); 
void treeprint(struct tnode *); 
int getword(char *,int); 
 
 
struct tnode *talloc(void); 
char *strdup2(char *); 
 
 
/*word frequency count*/ 
main() 
{ 
  struct tnode *root; 
  char word[MAXWORD]; 
 
  root=NULL; 
  while(getword(word,MAXWORD)!=EOF) 
    if(isalpha(word[0])) 
      root=addtree(root,word); 
  treeprint(root); 
  return 0; 
} 
 
#define BUFSIZE 100 
char buf[BUFSIZE];/*buffer for ungetch*/ 
int bufp=0;/*next free position in buf*/ 
 
int getch(void)/*get a (possibly pushed back) character*/ 
{ 
  return (bufp>0)? buf[--bufp]:getchar(); 
} 
 
void ungetch(int c)/*push back character on input*/ 
{ 
  if(bufp>=BUFSIZE) 
    printf("ungetch:too many characters\n"); 
  else 
    buf[bufp++]=c; 
} 
 
/*getword:get next word or character from input*/ 
int getword(char *word,int lim) 
{ 
  int c,getch(void); 
  void ungetch(int); 
  char *w=word; 
 
  while(isspace(c=getch() )); 
 
  if(c!=EOF) 
    *w++=c; 
  if(!isalpha(c)){ 
    *w='\0'; 
    return c; 
  } 
  for(;--lim>0;w++) 
    if(!isalnum(*w=getch())){ 
      ungetch(*w); 
      break; 
    } 
  *w='\0'; 
  return word[0]; 
} 
 
 
/*addtree:add a node with w,at or below p*/ 
struct tnode *addtree(struct tnode *p,char *w) 
{ 
  int cond; 
 
  if(p==NULL){/*a new word has arrived*/ 
    p=talloc();/*make a new node*/ 
    p->word=strdup(w); 
    p->count=1; 
    p->left=p->right=NULL; 
  }else if((cond=strcmp(w,p->word))==0) 
    p->count++;/*repeated word*/ 
  else if(cond<0)/*less than into left subtree*/ 
    p->left=addtree(p->left,w); 
  else  /*greater than into right subtree*/ 
    p->right=addtree(p->right,w); 
  return p; 
} 
/*treeprint:in-order print of tree p*/ 
void treeprint(struct tnode *p) 
{ 
  if(p!=NULL){ 
    treeprint(p->left); 
    printf("%4d %s\n",p->count,p->word); 
    treeprint(p->right); 
  } 
} 
 
#include 
/*talloc:make a tnode*/ 
struct tnode *talloc(void) 
{ 
  return (struct tnode *)malloc(sizeof(struct tnode)); 
} 
 
 
char *strdup2(char *s)/*make a duplicate of s*/ 
{ 
  char *p; 
 
  p=(char *)malloc(strlen(s)+1);/*+1 for '\0'*/ 
  if(p!=NULL) 
    strcpy(p,s); 
  return p; 
} 

其中，其它的关于union、enum这里就不多说了，再说一个关于结构体的非常重要的应用——位操作:

当然，我们知道，对于位操作，我们可通过#define tables（即用宏和C中的位操作来实现）

如:

#define KEYWORD 01 /*0001*/

#define EXTERNAL 02 /*0010*/

#define STATIC 04   /*0100*/

enum{KEYWORD =01,EXTERNAL =02,STATIC =04};

struct{

unsigned int is_keyword:1;

unsigned int is_extern:1;

unsigned int is_static:1;

}flags;/*This defines a variable called flags that contains three 1-bit fields*/

flags.is_extern=flags.is_static=1;

flags.is_extern=flags.is_static=0;