Compiler_词法分析_表驱动法

本文出自：http://blog.csdn.net/svitter
DFA：

使用了表驱动法；

构造的表如下：

表驱动

	num	.	E	+/-	other
0	1	6	-	-	-
1	1	2	5	-	-
2	2	-	3	-	-
3	-	-	-	4	--
4	5	-	-	-	-
5	5	-	-	-	-
6	2	-	-	-	-
7

代码如下：

//============================================================================
// Name        : compliler.cpp
// Author      : Vit
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include 
#include 
#include 
#include 

using namespace std;

int State[8][5];

//set final accept
const bool Acsta[7] =
{ 0, 1, 1, 0, 0, 1, 0, };

//JudgeNum
int JudgeNum(char &ch)
{
	if (ch >= '0' && ch <= '9')
		return 0;
	else if (ch == '.')
		return 1;
	else if (ch == 'E')
		return 2;
	else if (ch == '+' || ch == '-')
		return 3;
	else
		return 4;
}
//init the table
void init()
{
	//set error state
	for (int i = 0; i < 8; i++)
		for (int j = 0; j < 5; j++)
		{
			State[i][j] = 7;
		}

	//set table
	State[0][0] = 1;
	State[0][1] = 6;
	State[1][0] = 1;
	State[1][1] = 2;
	State[1][2] = 5;
	State[2][0] = 2;
	State[2][2] = 3;
	State[3][3] = 4;
	State[4][0] = 5;
	State[5][0] = 5;
	State[6][0] = 2;
}

//利用函数调用来读
char* Judge(char *str)
{
	int i, j; //work point

	//var
	int len = strlen(str); //计算串长度
	char *t = new char[2000]; //返回串
	memset(t, '\0', 2000);
	int cur; //字符下标
	char ch; //字符
	int state; //状态
	int beg; //开始
	int endd; //结束
	bool change;
	//start
	for (i = 0; i < len; i++)
	{
		beg = cur = i;
		ch = str[i];
		state = 0;
		endd = beg;
		change = false;
		while (state != 7)
		{
			state = State[state][JudgeNum(ch)];
			if (Acsta[state])
			{
				endd = cur; //记录最后一次符合状态的下标
				change = true;
			}
			ch = str[++cur];
			if (change)
			{
				if ((endd - beg) >= strlen(t))
				{
					for (j = beg; j <= endd; j++)
					{
						t[j - beg] = str[j];
					}
				}
				change = false;
			}
		}
	}
	return t;
}

int main(void)
{
	char *t;
	char str[2000];
	init();
	freopen("test", "r", stdin);
	while (~scanf("%s", str))
	{
		t = Judge(str);
		printf("%s\n", t);
	}
	return 0;
}