scanner.cpp

使用实际的编译算法的计算器 包括词法、文法分析过程

#include<cctype>
#include<stdlib.h>
#include"StdAfx.h"
#include"scanner.h"

MYSPC_BEGIN 
using std::string;

bool Scanner::Scan()
{
	_PreScan();
	DSTATE s;
	while(s=_NextTok())
		_ts.push(s);
	return _pos==_slen; //see : "case'$': _pos++; return EOI;"
}

void Scanner::_PreScan()
{
	int i=0;
	if((*_inPtr)[0]=='+')
		(*_inPtr)[i++]='@';
	if((*_inPtr)[0]=='-')
		(*_inPtr)[i++]='#';
	while(i<_slen-1){
		if( (*_inPtr)[i]=='(')
			if((*_inPtr)[i+1]=='+')
				(*_inPtr)[++i]='@';
			else 
				if((*_inPtr)[i+1]=='-')
					(*_inPtr)[++i]='#';
		i++;
	}
}

DSTATE Scanner::_NextTok()
{
	DSTATE s=START;
	string vbuf;
	while(_pos<_slen){
		switch (s){
			case START: 
				if( isdigit((*_inPtr)[_pos]) ) { s=BNAT; vbuf+=(*_inPtr)[_pos++];}
				else
					switch ((*_inPtr)[_pos]){
			            case'+': _pos++; return PLUS;
						case'-': _pos++; return MINUS;
						case'*': _pos++; return MUL;
						case'/': _pos++; return DIV;
						case'(': _pos++; return LP;
						case')': _pos++; return RP;
						case'@': _pos++; return POSI;
						case'#': _pos++; return NEG;
						case'$': _pos++; return EOI; // _pos should equal to _slen after this rather than _slen-1
						default: return DERROR;
				    }
				break;
			case BNAT: 
				if( isdigit((*_inPtr)[_pos]) ) vbuf+=(*_inPtr)[_pos++];
		        else 
					if((*_inPtr)[_pos]=='.') { s=MFLOAT; vbuf+=(*_inPtr)[_pos++];}
			        else{_vs.push(atof(vbuf.c_str())); return NAT;}
				break;
			case MFLOAT: 
				if( isdigit((*_inPtr)[_pos]) ) { s=BFLOAT; vbuf+=(*_inPtr)[_pos++];}
	            else return DERROR;
	     		break;
			case BFLOAT: 
				if( isdigit((*_inPtr)[_pos]) ) vbuf+=(*_inPtr)[_pos++];
				else{ _vs.push(atof(vbuf.c_str())); return FLOAT;}
				break;
		}		
	}
	return DERROR;
}

MYSPC_END