将C语言的声明翻译成通俗语言——cdecl

普通方法：

#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 now;

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

enum type_tag classify_string(void)
{
char *s = now.string;
if (!strcmp(s, "const"))
{
strcmp(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, "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)//读取下一个标记到now
{
char *p = now.string;
while ((*p = getchar()) == ' ');//跳过空白字符
if (isalnum(*p))
{
while (isalnum(*++p = getchar()));
ungetc(*p,stdin);//将不符合的字符退回输入流
*p = '\0';
now.type = classify_string();
return;
}
if (*p == '*')
{
strcpy(now.string, "pointer to");
now.type = '*';
return;
}
now.string[1] = '\0';//单字符标记
now.type = *p;
return;
}
void read_to_first_identifer()
{
gettoken();
while (now.type != IDENTIFIER)//找到标识符
{
push(now);
gettoken();
}
printf("%s is ", now.string);
gettoken();
return;
}
void deal_with_arrays()
{
while (now.type == '[')
{
printf("array ");
gettoken();//数字或']'
if (isdigit(now.string[0]))
{
printf("0..%d ", atoi(now.string) - 1);
gettoken();//读取']'
}
gettoken();//读取']'之后的再一个标记
printf("of ");
}
}
void deal_with_function_args()
{
while (now.type != ')')
gettoken();
gettoken();
printf("function returing ");
}
void deal_with_pointers()
{
while (stack[top].type == '*')
printf("%s ", pop.string);
}
void deal_with_declacrator()//处理标识符后可能存在的数组/函数
{
switch (now.type)
{
case '[':deal_with_arrays(); break;
case '(':deal_with_function_args();
}
deal_with_pointers();
while(top >= 0)//处理在读入标识符之前压入堆栈的符号
{
if (stack[top].type == '(')
{
pop;
gettoken();//读取')'之后的符号
deal_with_declacrator();
}
else
printf("%s ", pop.string);
}
}

int main()
{
read_to_first_identifer();
deal_with_declacrator();
printf("\n");
return 0;
}

有限自动机：

#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 now;

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

enum type_tag classify_string(void)
{
char *s = now.string;
if (!strcmp(s, "const"))
{
strcmp(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, "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)//读取下一个标记到now
{
char *p = now.string;
while ((*p = getchar()) == ' ');//跳过空白字符
if (isalnum(*p))
{
while (isalnum(*++p = getchar()));
ungetc(*p, stdin);//将不符合的字符退回输入流
*p = '\0';
now.type = classify_string();
return;
}
if (*p == '*')
{
strcpy(now.string, "pointer to");
now.type = '*';
return;
}
now.string[1] = '\0';//单字符标记
now.type = *p;
return;
}

void initialize(), get_array(), get_params(), get_lparen(), get_ptr_part(), get_type();
void(*nextstate)(void) = initialize;//设立一个函数指针表示状态

int main()
{
while (nextstate != NULL)
(*nextstate)();
return 0;
}

void initialize()//取最左边的标识符
{
gettoken();
while (now.type != IDENTIFIER)
{
push(now);
gettoken();
}
printf("%s is ", now.string);
gettoken();
nextstate = get_array;
}
void get_array()//查看标识符的下一个符号，如果是方括号
{
nextstate = get_params;
while (now.type == '[')
{
printf("array ");
gettoken();//一个数字或']'
if (isdigit(now.string[0]))
{
printf("0..%d ", atoi(now.string) - 1);
gettoken();//读取']'
}
gettoken();
printf("of ");
nextstate = get_lparen;
}
}
void get_params()//如果是一个左括号表示
{
nextstate = get_lparen;
if (now.type == '(')
{
while (now.type != ')')//到右括号为止的内容表示返回...的函数
gettoken();
gettoken();
printf("function returning ");
}
}
void get_lparen()//如果左边的符号是一个左括号
{
nextstate = get_ptr_part;
if (top >= 0)
{
if (stack[top].type == '(')
{
pop;
gettoken();//在')'后读取
nextstate = get_array;
}
}
}
void get_ptr_part()//如果左边的符号是下述之一:const,volatile,*
{
nextstate = get_type;
if (stack[top].type == '*')
{
printf("pointer to ");
pop;
nextstate = get_lparen;
}
else if (stack[top].type == QUALIFIER)
{
printf("%s", pop.string);
nextstate = get_lparen;
}
}
void get_type()//剩下的符号形成声明的基本类型
{
nextstate = NULL;
while (top >= 0)
{
printf("%s ", pop.string);
}
printf("\n");
}