C++ Expression::front方法代码示例

void evaluatePostfix(Expression postfix, std::string& evaluation)
{
  stack< std::string > evaluationStack;
  Token currentToken;
  std::string temp1;
  std::string temp2;
  std::string temp3;
  while(!postfix.isEmpty())
    {
      currentToken = postfix.front();
      postfix.pop();
      if(currentToken.getTokenType() == OPERAND)
	{
          evaluationStack.push(currentToken.getSymbol());
	}
      else
	{
	  temp1 = evaluationStack.pop();
          temp2 = evaluationStack.pop();
          temp3 = "(" + temp2 + currentToken.getSymbol() + temp1 + ")";
          evaluationStack.push(temp3);
	}
    }
  evaluation = evaluationStack.pop();
}

void convertToPostfix(Expression infix, Expression& postfix)
{
  stack<Token> conversionStack;
  Token currentToken;
  //infix.print(std::cout);
  Token noopToken;
  noopToken.setTokenType(OPERATOR);
  noopToken.setOperatorType(NOOP);
  noopToken.setSymbol("");
  conversionStack.push(noopToken);  
  while(!infix.isEmpty())
    {
      //      postfix.print(std::cout);
      currentToken = infix.front();
      infix.pop();
      // currentToken.print(std::cout);
          
      if(currentToken.getTokenType() == OPERAND)
	{
	  postfix.push(currentToken);
	}      
      else
	{
	   while(currentToken.getOperatorType() <= conversionStack.top().getOperatorType())
	     {
	       postfix.push(conversionStack.pop());
	     }
	   conversionStack.push(currentToken);
	}
    }

  while(!conversionStack.isEmpty())
    {
      if(conversionStack.top().getOperatorType() != NOOP)
	{
	  postfix.push(conversionStack.top());
	}
      conversionStack.pop();
    }
 
}

//Evaluate an equation in post fix
Cell* ExpParser::PostEval(Expression &post, bool bSymLoad)
{
	static TexAnchor constAncs[4];
	static bool ancsSet;
	if (!ancsSet)
	{
		constAncs[0] = TexAnchor(0,0); constAncs[1] = TexAnchor(1,0);
		constAncs[2] = TexAnchor(1,1); constAncs[3] = TexAnchor(0,1);
	}



	Expression temp;//a stack for operands

	while (!post.empty())
	{//there are more terms to evaluate
		Cell *cell = post.front();
		post.pop_front();
		char Operator = cell->op();

		if (Operator == 0)//if not operator
			temp.push_front(cell);//push it to the stack
		else if (Operator == 'C') 
		{
			Vec c;
			for (int i = 2; i >= 0; --i) // they come in reverse order
			{
				if (temp.empty())
					return NULL; // not enough arguments
				Cell *pc = temp.front();
				if (pc->cval() != NULL)
					return NULL; // Coord in Coord
				c[i] = pc->val();
				temp.pop_front();
			}
			temp.push_front(new CoordCell(c));
		}
		else if ((Operator == 'A') || (Operator == 'T'))
		{
			int n = (Operator == 'A')?4:3;
			SymCell *v[4] = {0}; // init to NULLs
			for (int i = n-1; i >= 0; --i) // they come in reverse order
			{
				if (temp.empty())
					return NULL; // not enough arguments
				Cell *pc = temp.front();
				if (pc->cval() == NULL)
					return NULL; // Coord in Coord
				temp.pop_front();
				v[i] = static_cast<SymCell*>(pc);
			}

			MyPolygon *poly = m_obj->AddPoly(v[0]->point(), v[1]->point(), v[2]->point(), (v[3] != NULL)?(v[3]->point()):NULL, constAncs);
			*m_decompile += (n == 4)?QString("add4("):QString("add3(");
			for(int i = 0; i < n; ++i)
			{
				DefPoint &def = (*g_symbols)[v[i]->clval()];
				def.used = true; // mark symbol as used
				poly->vtx[i]->col = def.color;

				*m_decompile += + v[i]->clval().c_str();
				if (i < n - 1) *m_decompile += ",";
			}
			*m_decompile += ")\n";

			temp.push_front(new NumCell(0));
		}
		else if (Operator == 'U') // color
		{
			// get paramtete
			if (temp.empty())
				return NULL; // not enough arguments
			Cell *pc = temp.front();
			// don't pop it
			if (pc->clval().size() == 0)
				return NULL; // not L-value (color ref)
			static_cast<SymCell*>(pc)->setColorRef(true);			
		}
		else
		{//evaluate the last two operands at the stack
			if (temp.empty())
				return NULL;
			Cell *n2 = temp.front();
			temp.pop_front();
			if (temp.empty())
				return NULL;
			Cell *n1 = temp.front();
			temp.pop_front();

			Cell *res;
			if ((cell->op() == '=') && (!bSymLoad)) // do not load symbol
				res = n2; // short circuit
			else
				res = Eval2(n1, cell, n2);

			if (res == NULL)
				return NULL;
			temp.push_front(res);
		}
//.........这里部分代码省略.........

//next step is to change it into post fix
bool ExpParser::In2Post(Expression &in, Expression &post)
{
	Expression temp;// a temp stack for operators

	while (!in.empty())
	{//there are more terms
		Cell *cell = in.front();
		in.pop_front();

		char Operator = cell->op();

		if (Operator == 0)//this is number
		{
			post.push_back(cell);//add as is
		}
		else if (isFunc(Operator))
		{
			temp.push_front(cell);
		}
		else if (Operator == ',')
		{
			while (!temp.empty() && (temp.front()->op() != '('))
			{//pops to the open bracket
				post.push_back(temp.front());
				temp.pop_front();
			} 
			if (temp.empty())
				return false; // missing parens
		}
		else if (Operator == ')')
		{
			while (temp.front()->op() != '(')
			{//pops to the open bracket
				post.push_back(temp.front());
				temp.pop_front();
			}
			temp.pop_front(); // pop '('
			if (!temp.empty() && (isFunc(temp.front()->op())))
			{
				post.push_back(temp.front());
				temp.pop_front();
			}
			// we already checked that there are enough parens.
		}
		else if (Operator == '(')
		{
			temp.push_front(cell);
		}
		else
		{//need to pop some operaotrs before putting my one
			while ((!temp.empty()) && 
				( (isLeftAss(Operator) && (opPriority(Operator) <= stackPriority(temp))) ||
				  (!isLeftAss(Operator) && (opPriority(Operator) < stackPriority(temp))) ))
			{
				post.push_back(temp.front());
				temp.pop_front();
			}
			temp.push_front(cell);
		}
	}
	while (!temp.empty())
	{//pops the rest of operators
		post.push_back(temp.front());
		temp.pop_front();
	}
	return true;
}

int stackPriority(Expression &s)
{//returns the priority of the element on the top 0 for an empty stack
	return s.empty()?0:opPriority(s.front()->op());
}