源码--函数申明分析

/*

摘自C专家编程
function name:declaration.c
description:函数申明分析
*/
#include
#include
#include
#include
#define MAXTOKENS 100
#define MAXTOKENLEN 64

enum type_tag {IDENTIFIER,QUALIFER,TYPE};

struct token {
 char type;
 char string[MAXTOKENLEN];
 };
 
 int top = -1;
 struct token stack[MAXTOKENS];
 struct token this;

#define pop stack[top--]
#define push(s) stack[++top] = s

/*推断标识符的类型*/
enum type_tag classify_string(void)
{
 char *s = this.string;
 if(!strcmp(s,"const")){
 strcpy(s,"read-only");
 return QUALIFER;
 }
 if(!strcmp(s,"volatile")) return QUALIFER;
 if(!strcmp(s,"void")) return TYPE;
 if(!strcmp(s,"char")) return TYPE;
 if(!strcmp(s,"signed")) return TYPE;
 if(!strcmp(s,"unsigned")) return TYPE;
 if(!strcmp(s,"short")) return TYPE;
 if(!strcmp(s,"int")) return TYPE;
 if(!strcmp(s,"long")) return TYPE;
 if(!strcmp(s,"float")) return TYPE;
 if(!strcmp(s,"double")) return TYPE;
 if(!strcmp(s,"struct")) return TYPE;
 if(!strcmp(s,"union")) return TYPE;
 if(!strcmp(s,"enum")) return TYPE;
 return IDENTIFIER;
}

/*读取下一个标记到"this"*/
void gettoken(void)
{
 char *p = this.string;
 
 /*略过空白字符*/
 while((*p = getchar()) == ' ');  //自解读：略过开始的空格符
 
 if(isalnum(*p)){ /*读入的标识符以字母或数字开头*/
  while(isalnum(*++p = getchar()));  //自解读：输入字符逐字符拷贝，遇到不是字母或数字就返回，意味着遇到空格就返回了。
  ungetc(*p,stdin);    //自解读：将当前字符退回stdin字符流
  *p = '\0';
  this.type = classify_string();
  return;
 }
 
 if(*p == '*'){
  strcpy(this.string,"pointer to");
  this.type = '*';
  return;
 }
 
 this.string[1]='\0';   //自解读：用于存储'('或'['
 this.type = *p;
 return;
 
}

/*理解所有分析过程的代码段*/
read_to_first_identifer(){
gettoken();
while(this.type != IDENTIFIER){
 push(this);
 gettoken();
}
printf("%s is ",this.string);
gettoken();

}

deal_with_arrays(){
while(this.type == '['){
 printf("array ");
 gettoken(); /*数字或？*/
 if(isdigit(this.string[0])){
 printf("0..%d ",atoi(this.string)-1);
 gettoken(); /*读取']'*/
 }
 gettoken();  /*读取']'之后的再一个标记*/
 printf("of ");
}

}

deal_with_function_args(){
 while(this.type != ')'){
  gettoken();
 }
 
 gettoken();
  printf("function returning ");
}

deal_with_pointers(){
 while(stack[top].type == '*'){
  printf("%s ",pop.string);
 }
}

/*处理标识符之后可能存在的数组/函数*/
deal_with_declarator(){
switch(this.type){
 case '[': deal_with_arrays();break;
 case '(': deal_with_function_args();
}

 deal_with_pointers();
 
 /*处理在读入到标识符之前压入到堆栈中的符号*/
 while(top >= 0){
 if(stack[top].type == '('){
 pop;
 gettoken();  /*读取')'之后的符号*/
 deal_with_declarator();
 }else{
  printf("%s ",pop.string);
 }
 }
 

}
 
main()
{
 int i;
  /*将标记压入堆栈中，直到遇见标识符*/
  read_to_first_identifer();
 
  i=top;
  while(i)
   printf("%s",stack[i--].string);
  printf("%s",stack[i].string);
  printf("\n");
  deal_with_declarator();
  printf("\n");
  return 0;
}