Lesson 21 Lexical analysis 词法分析器实现

#include <stdio.h>
#include "yy_nxt.c"
#include "yy_accept.c"

#define debug(fmt, args...)    fprintf(stderr, fmt, ##args)

int main(void)
{
    int state = 1;
    char buf[64];
    int i = 0;

    while (1)
    {
        char c;

        c = getchar();
        if (c == EOF)
            break;

        buf[i++] = c;

        debug("\tstate = %d, ", state);

        state = yy_nxt[state][c];

        debug("c = <%c>, new state = %d\n", c, state);

        if (state < 0)
        {
            int act = 0;

            state = -state;
            act = yy_accept[state];
            buf[i-1] = '\0';

            // 1: \n   21: space
            if (!(act == 1 || act == 21))
                printf("Pattern %d found! <%s>\n", act, buf);
            i = 0;

            state = 1;
            ungetc(c, stdin);
        }
    }

    return 0;
}
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约减转换表格，原来二维的转换表to一维数组 base/default/check/next
http://www.codingboy.com/zlog/post/32.html

http://bbs.zixia.net/boardcon.php?bid=571&id=230&ftype=6

http://m20.googlecode.com/svn/trunk/cc/scanner.l

注释flex生成代码
http://old.blog.edu.cn/user1/14610/archives/2005/376568.shtml

input/output/puton 字符串匹配问题
http://www.cnblogs.com/zhanglanyun/archive/2012/02/16/2354686.html
http://bbs.csdn.net/topics/300130885?jumpMenu=2&page=2

语法知识点

• 二维数组
• 二维函数指针数组
• 状态机编程之“机制和策略的分离”

  课堂讨论

• new_state 变量是否是必须的，如果去掉程序应该怎么改？

  课后练习

• 请根据第一节课介绍的 BNF 范式，对于词法分析器处理的结果，进行语法归约，看看是否满足C语法要求。