Lesson-21.md

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;
}

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。