bool CAG_RegEx::CreateNFA(string strRegEx)
{
// Parse regular expresion using similar
// method to evaluate arithmetic expressions
// But first we will detect concatenation and
// insert char(8) at the position where
// concatenation needs to occur
strRegEx = ConcatExpand(strRegEx);
cout<<strRegEx<<" : length "<<strRegEx.size()<<endl;
for(int i=0; i<strRegEx.size(); ++i)
{
// get the charcter
char c = strRegEx[i];
if(IsInput(c))
Push(c);
else if(m_OperatorStack.empty())
m_OperatorStack.push(c);
else if(IsLeftParanthesis(c))
m_OperatorStack.push(c);
else if(IsRightParanthesis(c))
{
// Evaluate everyting in paranthesis
while(!IsLeftParanthesis(m_OperatorStack.top()))
if(!Eval())
return false;
// Remove left paranthesis after the evaluation
m_OperatorStack.pop();
}
else
{
while(!m_OperatorStack.empty() && Presedence(c, m_OperatorStack.top()))
if(!Eval())
return false;
m_OperatorStack.push(c);
}
}
// Evaluate the rest of operators
while(!m_OperatorStack.empty())
if(!Eval())
return false;
// Pop the result from the stack
if(!Pop(m_NFATable))
return false;
// Last NFA state is always accepting state
m_NFATable[m_NFATable.size()-1]->m_bAcceptingState = true;
return true;
}
string CAG_RegEx::ConcatExpand(string strRegEx)
{
string strRes;
for(int i=0; i<strRegEx.size()-1; ++i)
{
char cLeft = strRegEx[i];
char cRight = strRegEx[i+1];
strRes += cLeft;
if((IsInput(cLeft)) || (IsRightParanthesis(cLeft)) || (cLeft == '*'))
if((IsInput(cRight)) || (IsLeftParanthesis(cRight)))
strRes += char(8);
}
strRes += strRegEx[strRegEx.size()-1];
return strRes;
}
