compile.cpp

一个小程序

//一遍编译器的实现文件

#include "compile.h"

//将 DIV,MOD两个记号插入
void translate::init()
{
	entry keywords[] =
	{
		"div", DIV,
		"mod", MOD,
		0,		0
	};

	entry *p;
	for( p = keywords; p->token; p++)
		insert(p->lexptr,p->token);
}
//-----------------------------------------------------

//查找标志符函数定义
int translate::lookup(char s[])
{
	int p;
	for(p = lastentry; p>0; p = p-1)
		if(strcmp(symtable[p].lexptr, s) == 0)
			return p;
	return 0;
} 
//------------------------------------------------------

//插入标志符函数的定义
int translate::insert(char s[],int tok)
{
	int len;
	len = strlen(s); //strlen 计算s的长度
	if(lastentry + 1 >= SYMMAX)
		error("lexemes table full");
	if(lastchar + len + 1 >= STRMAX)
		error("lexemes array full");

	lastentry = lastentry + 1;
	symtable[lastentry].token = tok;

	symtable[lastentry].lexptr = &lexemes[lastchar +1];
	lastchar = lastchar + len + 1;
	strcpy(symtable[lastentry].lexptr, s);

	return lastentry;
}
//------------------------------------------------------

//错误处理函数定义,输出错误显示的字符串
void translate::error(char *m)
{
	fprintf(stderr, "line %d: %s\n", lineno, m);
	return;  //非正常终止
}
//-------------------------------------------------------

// 后缀形式的成员函数输出
void translate::emit(int t, int tval)
{
	switch(t)
	{
	case '+':
	case '-':
	case '*':
	case '/':
		printf("%c\n",t);
		break;
	case DIV:
		printf("DIV\n");
		break;
	case MOD:
		printf("MOD\n");
		break;
	case NUM:
		printf("%d\n",tval);
		break;
	case ID:
		printf("%s\n",symtable[tval].lexptr);
		break;
	default:
		printf("token %d,tokenval %d\n", t, tval);
	}
}
//-----------------------------------------------------

//语法分析成员函数定义
int translate::lexan()
{
	int t;
	while(1)
	{
		t = getchar();
		if( t==' ' || t=='\t')
			;  //删去空白符
		else if(t == '\n')
			lineno = lineno + 1;
		else if(isdigit(t))
		{
			ungetc(t,stdin);
			scanf("%d",&tokenval);
			return NUM;
		}
		else if(isalpha(t))   //t是字母
		{
			int p, b = 0;
			while(isalnum(t))  //t是字母或数字
			{
				lexbuf[b] = t;
				t = getchar();
				b = b + 1;
				if (b >= BSIZE)
					error(" compiler error");
			}
			lexbuf[b] = EOS;
			if (t != EOF)
				ungetc(t, stdin);
			p = lookup(lexbuf);
			if (p == 0)
				p = insert(lexbuf, ID);
			tokenval = p;
			return symtable[p].token;
		}
		else if (t == EOF)
			return DONE;
		else
		{
			tokenval = NONE;
			return t;
		}
	}
}
//----------------------------------------------------

void translate::parse()	 //分析并翻译表达式列表
{
	lookahead = lexan();
	while (lookahead != DONE)
	{
		expr();
		match(';');
	}
}
//--------------------------------------------------------

//
void translate::expr()
{
	int t;
	term();
	while(1)
	{
		switch(lookahead)
		{
		case '+':
		case '-':
			t = lookahead;
			match(lookahead);
			term();
			emit(t,NONE);
			continue;
		default:
			return;
		}
	}
}
//-----------------------------------------------------

//
void translate::term()
{
	int t;
	factor();
	while(1)
	{
		switch(lookahead)
		{
		case '*':
		case '/':
		case DIV:
		case MOD:
			t = lookahead;
			match(lookahead);
			factor();
			emit(t,NONE);
			continue;
		default:
			return;
		}
	}
}
//-------------------------------------------------------

//
void translate::factor()
{
	switch(lookahead)
	{
	case '(':
		match('(');
		expr();
		match(')');
		break;
	case NUM:
		emit(NUM, tokenval);
		match(NUM);
		break;
	case ID:
		emit(ID, tokenval);
		match(ID);
		break;
	default:
		error("systax error");
	}
}
//------------------------------------------------------

//
void translate::match(int t)
{
	if (lookahead == t)
		lookahead = lexan();
	else
		error("syntax error");
}
//-------------------------------------------------------