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用FSM实现cdecl

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摘抄自《C语言专家编程》

  • 添加atoi()的头文件

  • 把this改成了thisss

  • 运行环境 gcc

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define MAXTOKENS 100
#define MAXTOKENLEN 64

enum type_tag { IDENTIFIER,QUALIFIER,TYPE};

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

int top = -1;

/*在第一个标识符(identifier)前保存所有的标记(token)*/
struct token stack[MAXTOKENS];
/*保存刚读入的标记*/
struct token thisss;

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

enum type_tag classify_string(void)
/*判断标识符的类型*/
{
    char *s = thisss.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)
{
    /*读入下一个标记，保存在"thisss"中*/
    char *p = thisss.string;
    /*略过所有的空白字符*/
    while((*p = getchar()) == ' ');
    if (isalnum(*p))
    {
        /*在标识符中读入A-Z,1-9字符*/
        while(isalnum( *++p = getchar() ) );
        ungetc(*p,stdin);
        *p = '\0';
        thisss.type = classify_string();
        return;
    }
    thisss.string[1] = '\0';
    thisss.type = *p;
    return;
}

void initialize(), get_array(), get_params(), get_lparen(), get_ptr_part(), get_type();

void (*nextstate)(void) = initialize;

int main(int argc, char const *argv[])
/*用有限状态机实现的cdecl*/
{
    /*在不同的状态中转换，直到指针为NULL*/
    while(nextstate != NULL)
    {
        (*nextstate)();
        return 0;
    }
}

void initialize()
{
    gettoken();
    while(thisss.type != IDENTIFIER)
    {
        push(thisss);
        gettoken();
    }
    printf("%s is",thisss.string);
    gettoken();
    nextstate = get_array;
}

void get_array()
{
    nextstate = get_params;
    while(thisss.type == '[')
    {
        printf("array ");
        gettoken();/*一个数字或']'*/
        if (isdigit(thisss.string[0]))
        {
            printf("0..%d\n", atoi(thisss.string) - 1 );
            gettoken();/*读取']'*/
        }
        gettoken();/*在']'之后读取*/
        printf("of ");
        nextstate = get_lparen;
    }
}

void get_params()
{
    nextstate = get_lparen;
    if (thisss.type == '(')
    {
        while(thisss.type != ')')
        {
            gettoken();
        }
        gettoken();
        printf("function returning ");
    }
}

void get_lparen()
{
    nextstate = get_ptr_part;
    if (top >= 0)
    {
        if (stack[top].type == '(')
        {
            pop;
            gettoken();/*在')'之后读取*/
            nextstate = get_array;
        }
    }
}

void get_ptr_part()
{
    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()
{
    nextstate = NULL;
    /*处理在读入标识符之前被放在堆栈里的所有标记*/
    while(top >= 0)
    {
        printf("%s ", pop.string);
    }
    printf("\n");
}