#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#define MAXTOKENS 100
#define MAXTOKENLEN 64
  
enum type_tag{IDENTIFIER, QUALIFIER, TYPE}; /*标识符，限定符，类型*/
  
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
  
#define STRCMP(a,R,b) (strcmp(a,b) R 0)
  
/*推断标识符类型*/
enum type_tag classify_string(void)
{
    char *s = this.string;
    if (STRCMP(s,==,"const"))
    {
        strcpy(s,"read-only");
        return QUALIFIER;
    }
    if (STRCMP(s,==,"volatile")) return QUALIFIER;
    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,==,"double")) return TYPE;
    if (STRCMP(s,==,"float")) 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"
*可能读入的字符包括：字母、数字、*[]()
*/
void gettoken(void)
{
    char *p = this.string;
      
    /*略过空白字符*/
    while((*p = (char)getchar()) == ' ') ;
      
    /*是字母或数字*/
    if (isalnum(*p))
    {
        while(isalnum(*++p = (char)getchar())) ; /*读到下一个不是字母或数字为止*/
        ungetc(*p,stdin);  /*将一个字符回退到输入流*/
        *p = '';
        this.type = (char)classify_string();
        return;
    }
      
    if (*p == '*')
    {
        strcpy(this.string,"pointer to");
        this.type = '*';
        return;
    }
      
    this.string[1] = '';
    this.type = *p;
    return;
}
  
/*理解所有分析过程的代码段*/
int read_to_first_identifier(void)
{
    gettoken(); /*取第一个标记*/
    while(this.type != (char)IDENTIFIER) /* 取到标识符终止，标识符未压入栈 */
    {
        push(this);
        gettoken();
    }
      
    printf("%s is ",this.string);
    gettoken();/*再取标识符右边一个符号*/
    return 0;
}
  
int deal_with_arrays(void)
{
    while(this.type == '[')
    {
        printf("array ");
        gettoken();/*数字域或']'*/
        if (isdigit(this.string[0]))
        {
            printf("0..%d ",atoi(this.string)-1);
            gettoken(); /*取']'*/
        }
          
        gettoken(); /* 读取']'后的下一个标记，可能还是一个'[' */
        printf("of ");
    }
      
    return 0;
}
  
int deal_with_function_args(void)
{
    while(this.type != ')') /* 把函数参数取出来丢弃 */
    {
        gettoken();
    }
      
    gettoken(); /* 读取')'后的下一个标记 */
    printf("function returning ");
    return 0;
}
  
int deal_with_pointers(void)
{
    while(stack[top].type == '*')
    {
        printf("%s ",pop.string);
    }
    return 0;
}
  
int deal_with_declarator(void)
{
    /*处理标识符后可能存在的数组或函数*/
    switch(this.type)
    {
        case '[' : deal_with_arrays();break;
        case '(' : deal_with_function_args();break;
        default : break;
    }
      
    deal_with_pointers(); /* 栈顶元素是'*' */
      
    /*处理在读到标识符之前压入堆栈的符号*/
    while(top >= 0)
    {
        if (stack[top].type == '(')
        {
            pop;
            gettoken(); /* 读取')'之后的符号，可能是'('或'[' */
            deal_with_declarator();  /* 递归调用 */
        }
        else
        {
            printf("%s ",pop.string);
        }
    }
      
    return 0;
}
  
int main(void)
{
    /*将标记压入堆栈中，直到遇见标识符*/
    read_to_first_identifier();
    deal_with_declarator();
    printf("n");
      
    return 0;
}