getfirst.cpp

这是编译原理编译器中的一部分

#include "parse.h"
#include "read.h"
#include "make.h"

extern vecNter nonterminals;

vector<string> makeFirst(vector<string> vecstr )
{
	vector<string> first;int i;
	for( i = 0;i < (int)vecstr.size();i++)
	{
		if( findIndex(vecstr[i] ) == -1 )
		{
			if ( !hasexisted( first,vecstr[i] ) ) 
				first.push_back(vecstr[i]);
			break;
		}//if
		else
		{
			int index = findIndex( vecstr[i] );                
			add( nonterminals[index].first,first );
			if( !hasexisted( nonterminals[ index ].first,  "ε" ) )break;
		}//else
	}//for

	if( i == vecstr.size() )first.push_back("ε");
	return first;
}

void add(vector<string>  &v1,vector<string> &v2)
{
	for(int i = 0;i <(int) v1.size();i++)
		if( v1[i] != "ε" && !hasexisted(v2,v1[i]) )v2.push_back(v1[i]);
}