【C++】词法分析器

(代码在在最后面)

实验目的

熟悉词法分析阶段的要求，掌握利用状态图手工实现词法分析器的方法。

实验设备

硬件：PC 机一台

软件：Windows系统，高级语言集成开发环境

实验内容

根据词法要求手工实现词法分析器

实验要求及步骤

1. 理解以下词法表述和状态图表示。

2. 参考教科书3.2.4章节编写代码实现词法分析器。实现语言不限，推荐使用C语言，不可用脚本类语言；不允许使用任何语言的正规式控件实现实验要求。

3. 提交词法分析器代码与实验报告。实验报告为word形式文档，内容是10对如下形式的输入输出。

if(7xx)=8xx

%%

910x*=200

(7x+8y)=60

__fxk/10

99910

$666+(10)x

jihuiting = dameinv

%%680x1**((55)+x)

top 66

代码

#include<bits/stdc++.h>
using namespace std;
const int maxn = 1e5;
string input;
vector<string>errs;
typedef struct node
{
	int num;
	string content;
	string zhu;
	node(int a, string b)
	{
		this->num = a;
		if (a == 0)
			return;
		this->content = b;
		vector<string>v = { "","$dim","$if" ,"$do" ,"$stop" ,"$end" ,"$id" ,"$int","$assign","$plus","$star","$power","$comma","$lpar" ,"$rpar" ,"$err" };
		this->zhu = v[a];
		input.erase(0, b.length());
		if (this->num)
			this->print();
	}
	void print()
	{
		cout.setf(std::ios::left);
		cout << setw(20) << this->zhu;
		if (this->num == 6 || this->num == 7 || this->num == 15)
			cout << this->content;
		cout << endl;
	}
}node;

const vector<char>end_option = { '=','+','*',',','(',')' ,' ' };
node getnum(string a)
{
	string num = "";
	for (int i = 0; i < a.length() && isdigit(a[i]); i++)
	{
		num += a[i];
	}
	bool isnum = false;
	for (auto x : end_option)
	{
		if (a[num.length()] == x)
		{
			isnum = true;
			break;
		}
	}
	if ((num == "" || !isnum) && a.length() != num.length())
		return node(0, num);
	else
		return node(7, num);
}

node getword(string a)
{
	string word = "";
	for (int i = 0; i < a.length() && isalpha(a[i]); i++)
	{
		word += a[i];
	}
	vector<string> words = { "if","do","stop","end" };
	vector<string> words2 = { "IF","DO","STOP","END" };
	vector<int>num = { 2,3,4,5 };
	for (int i = 0; i < words.size(); i++)
	{
		if (word == words[i] || word == words2[i])
			return node(num[i], word);
	}
	return node(0,"");
}
node getoption(string a)
{
	vector<string> word = { "**","=","+","*",",","(",")" };//**要放在*前面
	vector<int>num = { 11,8,9,10,12,13,14 };
	for (int i = 0; i < word.size(); i++)
	{
		if (a.substr(0, word[i].length()) == word[i])
			return node(num[i], word[i]);
	}
	return node(0, "");
}
node getname(string a)
{
	if (isdigit(a[0]))
		return node(0, "");
	string name = "";
	for (int i = 0; i < a.length() && (isalnum(a[i])||a[i]=='_'||a[i]=='$'); i++)
	{
		name += a[i];
	}
	if (name == "")
		return node(0, "");
	return node(6, name);
}
node getother(string a)
{
	string other = "";
	for (int i = 0; i < a.length(); i++)
	{
		for (int j = 0; j < end_option.size(); j++)
		{
			if (a[i] == end_option[j])
			{
				errs.push_back(other);
				return node(15, other);
			}
		}
		other += a[i];
	}
	errs.push_back(other);
	return node(15, other);
}
int main()
{
	getline(cin, input);
	//判断顺序：
	//数字(7) getnum
	//单词(2-5) getword
	//符号(8-14) 
	//标识符(6)
	//其他(15)
	while (input!="")
	{
		if (input[0] == ' ')
		{
			input.erase(0, 1);
			continue;
		}
		if (getnum(input).num)
			continue;
		if (getword(input).num)
			continue;
		if (getoption(input).num)
			continue;
		if (getname(input).num)
			continue;
		getother(input);
	}

	if (errs.size())
	{
		cout << "========错误分析报告========" << endl;
		for (auto x : errs)
		{
			cout << x << endl;
		}
	}
}