C语言词法分析器(C++语言实现)

C语言词法分析器(C++语言实现)

这是老师布置的编译原理的实验课任务,课余时间花了近一个星期的时间去编写代码(主要是C++太久没有用了,好多函数都不熟悉,查阅了很多资料),这次的词法分析没有语法错误判断功能,如果想要增加功能可以在相关函数代码段增加即可.

c语言词法分析流程如图所示:

代码如下:这次的代码算是我对代码整洁之道前期知识的一个练习,特别是变量的命名以及函数的编写,如果觉得写的不错可以看看我关于代码整洁之道的相关文章

这次的代码基本没有写注释,但是我相信大家结合流程图也能看懂,如果觉得太长可以将代码复制到visual studio中将函数代码块闭合起来这样看起来就逻辑清楚了

#include <iostream>
#include <string>
#include <map>
#include <ctype.h>
#include <algorithm>
using namespace std;
string readFile(string fileName);
string fileFilter();
string singleLineCommentsFilter();
string multilineCommmentsFileter();
string specialCharacterFilter();
void separateAndJudge();
bool isReservedWord(string vocabulary);
void separateAndJudge();
void showTokenData();
int digitStarted(int cnt);
bool isBoundSymbol(char ch);
bool isOperator(char ch);
int judgeStartingCharactorType(char ch);
bool isDigit(char ch);
bool isAlpha(char ch);
int alphaStarted(int cnt);
int underlineStarted(int cnt);
string transCharToString(char ch);
string codeSource;
map<string, int> tokens;//identifier is 1,reservedWord 2,digit 3,borderSymbol 4,operator 5
int main()
{
	codeSource = readFile("h:\\testCode.txt");
	cout << "This is source code" << endl << "---------------------------------" << endl << endl;
	cout << codeSource << endl;

	cout << "This is code filtered" << endl << "---------------------------------" << endl ;
	codeSource = fileFilter();
	codeSource = fileFilter();
	cout << codeSource << endl;

	separateAndJudge();

	cout << "this is tokens " << endl;
	showTokenData();
	return 0;
}


string readFile(string fileName)
{
	FILE* fp;
	if ((fp = fopen(fileName.c_str(), "r")) == NULL)
	{
		cout << "cant open file";
		exit(0);
	}
	else
	{
		string codeSource;
		char ch;
		while ((ch = fgetc(fp)) != EOF)
		{
			codeSource += ch;
		}
		return codeSource;
	}
};
string fileFilter()
{
	string filteredCode = singleLineCommentsFilter();
	filteredCode = multilineCommmentsFileter();
	filteredCode = specialCharacterFilter();
	return filteredCode;
};
void separateAndJudge()
{
	int cnt = 0;
	for (; cnt < codeSource.length(); cnt++)
	{
		int nowCnt = 0;
		while (codeSource[cnt] != ' ' and cnt < codeSource.length())
		{
			string a = "";
			switch (judgeStartingCharactorType(codeSource[cnt]))
			{
			case 1:
				cnt = digitStarted(cnt);
				break;
			case 2:
				cnt = alphaStarted(cnt);
				break;
			case 3:
				cnt = underlineStarted(cnt);
				break;
			case 4:		
				tokens[transCharToString(codeSource[cnt])] = 4;
				cnt++;
				break;
			case 5:				
				tokens[transCharToString(codeSource[cnt])] = 5;
				cnt++;
				break;
			case 6:
				cout << "wrong grammer" << endl;
				exit(0);
				cnt++;
				break;
			default:
				cnt++;
				break;
			}
			
		}
	}
}
void showTokenData()
{
	
	map<string, int>::iterator iter;

	for (iter = tokens.begin(); iter != tokens.end(); iter++)

		cout << iter->first << ' ' << iter->second << endl;
}


string singleLineCommentsFilter()
{
	long cnt = 0;
	for (; cnt < codeSource.length(); cnt++)
	{
		while (codeSource[cnt] == '/' and codeSource[cnt + 1] == '/' and cnt < codeSource.length())
		{
			while (codeSource[cnt] != '\n')
			{
				codeSource.erase(cnt, 1);
			}
		}
	}
	return codeSource;
}
string multilineCommmentsFileter()
{
	int cnt = 0;
	for (; cnt < codeSource.length(); cnt++)
	{
		if (codeSource[cnt] == '/' and codeSource[cnt + 1] == '*' and cnt < codeSource.length())
		{
			do
			{
				codeSource.erase(cnt, 1);
				if (codeSource[cnt+2]==EOF)
				{
					cout << "multilineCommments wrong" << endl;
					exit(0);
				}
			} while (codeSource[cnt + 2] != '*' and codeSource[cnt + 3] != '/');
			codeSource.erase(cnt, 4);
		}

	}
	return codeSource;
}
string specialCharacterFilter()
{
	for (int cnt = 0; cnt < codeSource.length(); cnt++)
	{
		if (codeSource[cnt] == '\n' or codeSource[cnt] == '\t' or codeSource[cnt] == '\v' or codeSource[cnt] == '\r')
		{
			codeSource.erase(cnt, 1);
			cnt--;
		}
	}
	return codeSource;
}


int judgeStartingCharactorType(char ch)
{
	int type = 0;
	if (isDigit(ch)) { type = 1; }
	else
	{
		if (isAlpha(ch)) { type = 2; }
		else
		{
			if (ch == '_') { type = 3; }
			else
			{
				if (isBoundSymbol(ch)) { type = 4; }
				else
				{
					if (isOperator(ch)) { type = 5; }
					else { type = 6; }
				}
			}
		}
	}
	return type;
}

int digitStarted(int cnt)
{
	string digit;
	digit += codeSource[cnt];
	cnt++;
	while (isDigit(codeSource[cnt]) or codeSource[cnt] == '.')
	{
		digit += codeSource[cnt];
		++cnt;
	}
	tokens[digit] = 3;
	return cnt;
}
int alphaStarted(int cnt)
{
	string alpha;
	alpha += codeSource[cnt];
	cnt++;
	while (isAlpha(codeSource[cnt]) or isDigit(codeSource[cnt])  or codeSource[cnt]=='_')
	{
		alpha += codeSource[cnt];
		++cnt;
	}
	if (isReservedWord(alpha)) { tokens[alpha] = 2; }
	else { tokens[alpha] = 1; }
	return cnt;
}
int underlineStarted(int cnt)
{
	string word;
	word += codeSource[cnt];
	cnt++;
	while (isAlpha(codeSource[cnt]) or isDigit(codeSource[cnt]))
	{
		word += codeSource[cnt];
		++cnt;
	}
	tokens[word] = 1;
	return cnt;
}


string transCharToString(char ch)
{
	string temp = " ";
	temp[0] = ch;
	return temp;
}


bool isReservedWord(string vocabulary)
{
	string reserveWords[32] = {
	 "auto", "break", "case", "char", "const", "continue",
	"default", "do", "double", "else", "enum", "extern",
	"float", "for", "goto", "if", "int", "long",
	"register", "return", "short", "signed", "sizeof", "static",
	"struct", "switch", "typedef", "union", "unsigned", "void",
	 "volatile", "while"
	};
	bool flag = false;
	for (int i = 0; i <32 ; i++)
	{
		if (reserveWords[i]==vocabulary)
		{
			flag = true;
		}
	}
	return flag;
};

bool isBoundSymbol(char ch)
{
	string temp = "";
	temp += ch;
	bool flag = false;
	string boundSymbol[6] =
	{
		"(",   ")",   ",",   ";",  "{",  "}"
	};
	for (int i = 0; i < 6; i++)
	{
		if (boundSymbol[i] == temp)
		{
			flag = true;
		}
	}
	return flag;
}
bool isOperator(char ch)
{
	string temp = to_string(ch);
	bool flag = false;
	string operators[9] =
	{
		"+","-","*","/","=","%",">","<","=",
	};
	for (int i = 0; i < 9; i++)
	{
		if (operators[i] == temp)
		{
			flag = true;
		}
	}
	return flag;
}
bool isDigit(char ch)
{
	bool flag = false;
	if (ch >= '0' and ch <= '9')
	{
		flag = true;
	}
	return flag;
}
bool isAlpha(char ch)
{
	bool flag = false;
	if ((ch >= 'a' and ch <= 'z') or (ch >= 'A' and ch <= 'Z'))
	{
		flag = true;
	};
	return flag;
}