tjyj.cpp

2. 数据结构：设计存储中间结果及中间代码(四元式)的数据结构； 3. 算法：递归下降分析法的实现；

#include<iostream.h>
#include<fstream.h>
#include<string.h>

#define $ASSIGN 249
#define $IF 250
#define $THEN 251
#define $ELSE 252
#define $GREAT 253
#define $ID 254

//有效字符串: IF,ELSE,THEN, a,b,x,>,=
/*文法:
  S->id=id | if E then S else S
  E->id < id
*/

typedef struct Token
{
	int type;
	char ch;
}Token;

typedef enum{JUMP,JG,ASSIGN,END}OpKind;
typedef struct
{
	int label;			//标号
	OpKind op;
	char par1,par2;
	union
	{
		char result;
		int address;
	};
}Quad;					//四元式

#define MAX_TOKEN 256  //Token表大小
#define MAX_QUAD 256   //四元式数组大小

Token tokentable[MAX_TOKEN];
Quad quad[MAX_QUAD];
int token_index;       //token表索引
int total_len;         //token表有效长度

int quad_len;          //四元式表有效长度
int quad_index;        //四元式索引

int label;
ifstream ins;

bool init(char filename[255]);
bool cifa();

void ERROR();
void S(int,int);

void E(int,int,int);
bool nexttoken();
int newlabel();
void yuyi();

void printQuad();
void main()
{
	cout<<"请输入文件名:";
	char fname[200];
	cin>>fname;
	if(!init(fname))
		return;
	if(!cifa())
		return;
	char ch;
	while(1)
	{
		if(ins.eof())
			break;
		ins>>ch;
	}
	cout<<"词法分析结果:"<<endl;
	nexttoken();
	cout<<endl;
	cout<<"使用的产生式:"<<endl;
	yuyi();
	cout<<endl;
	cout<<"产生的四元式:"<<endl;
	printQuad();
}
int newlabel()
{
	return label++;
}
bool init(char filename[255])
{
	token_index=0;
	total_len=0;
	quad_len=0;
	quad_index=0;
	label=0;
	ins.open(filename,ios::nocreate | ios::in);
	if(ins.fail())
	{
		cout<<"打开文件出错!"<<endl;
		return false;
	}
	return true;
}

bool cifa()
{
	char buf[16];
	char ch;
	while(1)
	{
		ins>>ch;
		if(ins.fail())
			break;
		if(ch=='I')
		{
			ins>>buf;
			if(strcmp(buf,"F")==0)
				tokentable[total_len++].type=$IF;
		}
		else if(ch=='T')
		{
			ins>>buf;
			if(strcmp(buf,"HEN")==0)
				tokentable[total_len++].type=$THEN;
		}
		else if(ch=='E')
		{
			ins>>buf;
			if(strcmp(buf,"LSE")==0)
				tokentable[total_len++].type=$ELSE;
		}
		else if(ch=='>')
		{
			tokentable[total_len++].type=$GREAT;
		}
		else if(ch=='=')
		{
			tokentable[total_len++].type=$ASSIGN;
		}
		else if(ch=='x' || (ch>='a' && ch<='z'))
		{
			tokentable[total_len].type=$ID;
			tokentable[total_len++].ch=ch;
		}
	}
	return true;
	
}

#define AD_RESULT(nlabel,nop,npar1,npar2,nresult) {quad[quad_len].label=nlabel; quad[quad_len].op=nop; quad[quad_len].par1=npar1; quad[quad_len].par2=npar2; quad[quad_len].result=nresult; quad_len++; }
#define AD_ADDRESS(nlabel,nop,npar1,npar2,naddress) {	quad[quad_len].label=nlabel; 	quad[quad_len].op=nop; 	quad[quad_len].par1=npar1; 	quad[quad_len].par2=npar2; 	quad[quad_len].address=naddress; 	quad_len++; }

Token cur;
bool nexttoken()
{
	if(token_index>=total_len)
		return false;
	cur.type=tokentable[token_index].type;
	cur.ch=tokentable[token_index].ch;
	token_index++;
	return true;
}

void ERROR(char str[20])
{
	cout<<"error!  "<<str<<endl;
}

void S(int begin,int next)
{

	if(cur.type==$ID)
	{
		char a,b;
		cout<<"S->"<<cur.ch;
		a=cur.ch;
		if(!nexttoken())
			ERROR("S");
		if(cur.type!=$ASSIGN)
			ERROR("S");
		cout<<"=";
		if(!nexttoken())
			ERROR("S");
		if(cur.type!=$ID)
			ERROR("S");
		cout<<cur.ch<<endl;
		b=cur.ch;
		AD_RESULT(begin,ASSIGN,b,0,a);
		AD_ADDRESS(-1,JUMP,0,0,next);
		nexttoken();
	}
	else if(cur.type==$IF)
	{
		if(!nexttoken())
			ERROR("S");
		{
			cout<<"S->if E then S else S"<<endl;
			int etrue=newlabel();
			int efalse=newlabel();
			
			E(begin,etrue,efalse);
			if(cur.type==$THEN)
			{
				if(!nexttoken())
				ERROR("S");
				
				S(etrue,next);

				if(cur.type==$ELSE)
				{
					if(!nexttoken())
					ERROR("S");
					S(efalse,next);
				}
				else
				{
					ERROR("S");
				}
			}
			else
				ERROR("S");
		}
	}
}

void E(int begin,int etrue,int efalse)
{
	if(cur.type==$ID)
	{
		char a,b;
		a=cur.ch;
		cout<<"E->"<<cur.ch<<">";
		if(!nexttoken())
			ERROR("E()");
		if(cur.type!=$GREAT)
			ERROR("E()");
		if(!nexttoken())
			ERROR("E()");
		if(cur.type!=$ID)
			ERROR("E()");
		cout<<cur.ch<<endl;
		b=cur.ch;

		AD_ADDRESS(begin,JG,a,b,etrue);
		AD_ADDRESS(-1,JUMP,0,0,efalse);
		if(!nexttoken())
			ERROR("E()");
	}
	else
		ERROR("E()");
}

void yuyi()
{
	S(-1,1000);
	AD_RESULT(1000,END,0,0,'-');
}

void printQuad()
{
	for(int i=0;i<quad_len;i++)
	{
		if(quad[i].label>-1)
			cout<<"L"<<quad[i].label<<":";
		else cout<<"     ";
		if(quad[i].op==JG)
		{
			cout<<"J>,"<<quad[i].par1<<","<<quad[i].par2<<",L"<<quad[i].address<<endl;
		}
		else if(quad[i].op==JUMP)
		{
			cout<<"J ,"<<"-,-,L"<<quad[i].address<<endl;
		}
		else if(quad[i].op==ASSIGN)
		{
			cout<<"= ,"<<quad[i].par1<<",-,"<<quad[i].result<<endl;
		}
		else if(quad[i].op==END)
		{
			cout<<"-,-,-,-"<<endl;
		}
	}
}