main.cpp

词法分析器(编译原理)

/////////////////////////////////////////////////////////////////////////////////////
// Writing in C++

#include <fstream.h>  //文件流类定义在此头文件内
#include <string.h>

char chinput;   
int ipointer;
char* word;      
char* string;     

void GetChar()
{
	chinput=*(string+ipointer++);
}

void Retract()
{
	if((chinput==' '||chinput=='\t'||chinput=='\n')?false:true)
	{
		ipointer--;
		chinput='\0';
	}
}

void main()
{
	char filename[128];
	cout<<"Please input the name of the file you want to open:";
	cin>>filename;
	ifstream openFile(filename);
	if(openFile.fail())
	{
		cout<<"Error! Cannot open given file.\n";
		return;
	}
	while(openFile.peek()!=EOF)
	{
		openFile.ignore();
		ipointer++;
	}
	string=new char[ipointer+1];
	openFile.seekg(0);
	openFile.read(string,ipointer);
	*(string+ipointer)='\0';
	chinput='\0';
	ipointer=0;
	cout<<"Source codes in given file are:\n"<<string<<endl;
	char* temp=new char[2];
	GetChar();
	while(chinput!='\0')
	{		
		switch(chinput)
		{
		
		case ';':
			{
				cout<<"(4,\";\")"<<endl;
				break;
			}
		case '{':
			{
				cout<<"(5,\"{\")"<<endl;
				break;
			}
		case '}':
			{
				cout<<"(6,\"}\")"<<endl;
				break;
			}
		case '(':
			{
				cout<<"(7,\"(\")"<<endl;
				break;
			}
		case ')':
			{
				cout<<"(8,\")\")"<<endl;
				break;
			}
		case '+':
			{
				cout<<"(10,\"+\")"<<endl;
				break;
			}
		case '*':
			{
				cout<<"(11,\"*\")"<<endl;
				break;
			}
		case '=':
			{
				GetChar();
				if(chinput=='=')
				{
					cout<<"(13,\"==\")"<<endl;
				}
				else
				{
					cout<<"(12,\"=\")"<<endl;
					Retract();
				}
				break;
			}
		case '>':
			{
				GetChar();
				if(chinput=='=')
				{
					cout<<"(13,\">=\")"<<endl;
				}
				else
				{
					cout<<"(13,\">\")"<<endl;
					Retract();
				}
				break;
			}
		case '<':
			{
				GetChar();
				if(chinput=='>')
				{
					cout<<"(13,\"<>\")"<<endl;
				}
				else if(chinput=='=')
				{
					cout<<"(13,\"<=\")"<<endl;
				}
				else
				{
					cout<<"(13,\"<\")"<<endl;
					Retract();
				}
				break;
			}
	
		case '-':
			{
				GetChar();
				if((chinput>='0'&&chinput<='9')?true:false)
				{
					word=new char[128];
					*word='\0';								
				    *temp=chinput;
					*(temp+1)='\0';
					strcat(word,temp);
					GetChar();
					cout<<"(15,\"-"<<word<<"\")"<<endl;
				}
				else
				{
					cout<<"error,\"-\""<<endl;
					Retract();
				}
				break;
			}
		default:
			{
				if((chinput==' '||chinput=='\t'||chinput=='\n')?true:false)
					break;
				else if((chinput>='0'&&chinput<='9')?true:false)
				{
					word=new char[128];
					*word='\0';
				    *temp=chinput;
					*(temp+1)='\0';
					strcat(word,temp);
					GetChar();					
					cout<<"(15,\""<<word<<"\")"<<endl;
					Retract();
					break;
				}
				else if(((chinput>='a'&&chinput<='z')||(chinput>='A'&&chinput<='Z'))?true:false())
				{
					word=new char[128];
					*word='\0';		
					while((chinput>='0'&&chinput<='9')?true:false||((chinput>='a'&&chinput<='z')||(chinput>='A'&&chinput<='Z'))?true:false)
					{
						*temp=chinput;
						*(temp+1)='\0';
						strcat(word,temp);
						GetChar();
					}
					if(strcmp(word,"if")==0)
					{
						cout<<"(0,\""<<word<<"\")"<<endl;
					}
					else if(strcmp(word,"else")==0)
					{
						cout<<"(1,\""<<word<<"\")"<<endl;
					}
					else if(strcmp(word,"while")==0)
					{
						cout<<"(2,\""<<word<<"\")"<<endl;
					}
					else if(strcmp(word,"do")==0)
					{
						cout<<"(3,\""<<word<<"\")"<<endl;
					}
					else
					{
						cout<<"(14,\""<<word<<"\")"<<endl;
					}
					Retract();
					break;
				}
				else
				{
					cout<<"error,\""<<chinput<<"\""<<endl;
					break;
				}
			}
		}
		word=NULL;
		GetChar();
	}
	cout<<"词法分析结束，谢谢！";
}

// 该程序没能将“赋值语句”辨认出来，希望老师帮忙修改后发回，谢谢！：）