学步园

#include<stdio.h>
#include<string.h>
#include<ctype.h>
#include<stdlib.h>
#define MAXTOKENS 100
#define MAXTOKENLEN 64

enum type_tag {IDENTIFIER,QUALIFIER,TYPE};

struct token
{
char type;
char string[MAXTOKENLEN];
};

int top = -1;
struct token stack[MAXTOKENS];
struct token this;

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

enum type_tag classify_string(void)
//推断标识符的类型
{
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,"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;
}

void gettoken(void) //赌气下一个标记到"this"
{
char *p = this.string;

//略过空白字符
while((*p = getchar()) == ' ');

if(isalnum(*p))
{
//读入的标识符以A-Z,0-9开头
while(isalnum(*++p = getchar()));
ungetc(*p,stdin);
*p = '/0';
this.type = classify_string();
return;
}
if(*p == '*')
{
strcpy(this.string,"pointer to");
this.type = '*';
return;
}
this.string[2] = '/0';
this.type = *p;
return;
}

void read_to_first_identifier()
{
gettoken();
while(this.type != IDENTIFIER)
{
push(this);
gettoken();
}
printf("%s is ",this.string);
gettoken();
}

void deal_with_arrays()
{
while(this.type == '[')
{
printf("array");
gettoken();
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 ");
}
}

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

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

void deal_with_declarator()
{
//处理标识符之后可能存在的数组/函数
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);
}
}
}

int main()
{
//将标记压入堆栈中，知道遇见标识符
read_to_first_identifier();
deal_with_declarator();
printf("/n");
return 0;
}

cdecl，学习c/c++的一个小工具，可以将声明转换成白话文的形式，方便理解。此代码在vc++6.0，codeblocks10.05，dev-cpp4.9上均编译通过。