Not able to recognize "-"

[munna]

Hi,

I am using Qt 3 and trying a parse a string entered by the user. For this i am extracting each character and playing with it. The problem is when i try to compare a QString which is contains "-" with "-" the result is false.

Has someone encountered this kind of problem ? Am I doing something wrong? Here is the code:

for(pos=0;pos<expr.length();pos++)
{
       QString curr = expr.at(pos);	
	if(curr == ":")
	{
		OperatorParse("+");
	}
	else if((curr == QString(QChar(0xD7)))||(curr==QString(QChar(0xDD)))||
	(curr == "+")||(curr == "-")||(curr == "*")||(curr == "/")||(curr == "^"))
	{
		OperatorParse(curr);
	}
	else if(curr == "(")
	{
		LeftParse(0, pos);
	}
	else if(curr == "{")
	{
		LeftParse(1, pos);
	}
	else if(curr == "[")
	{
		LeftParse(2, pos);
	}
	else if((curr == ")")||(curr == "}")||(curr == "]"))
	{
		RightParse();
	}
}

for(pos=0;pos<expr.length();pos++)
{
       QString curr = expr.at(pos);	
	if(curr == ":")
	{
		OperatorParse("+");
	}
	else if((curr == QString(QChar(0xD7)))||(curr==QString(QChar(0xDD)))||
	(curr == "+")||(curr == "-")||(curr == "*")||(curr == "/")||(curr == "^"))
	{
		OperatorParse(curr);
	}
	else if(curr == "(")
	{
		LeftParse(0, pos);
	}
	else if(curr == "{")
	{
		LeftParse(1, pos);
	}
	else if(curr == "[")
	{
		LeftParse(2, pos);
	}
	else if((curr == ")")||(curr == "}")||(curr == "]"))
	{
		RightParse();
	}
}

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expr is the string that i am parsing.
I entered "2 - 2" but the - is not recongnized

Thanks

[wysota]

I guess this would be more efficient:

for(pos=0;pos<expr.length();pos++){
  const char curr = expr[pos];
  switch(curr){
  case ':': 
    OperatorParse('+');break;
  case '+': 
  case '-':  
  case '*':  
  case '/': 
  case '^': 
    OperatorParse(curr); break;
  case '(': 
    LeftParse(0, pos); break;
  case '{': 
    LeftParse(1, pos); break;
  case '[': 
    LeftParse(2, pos); break;
  case ')': 
  case '}': 
  case ']': 
    RightParse(); break;
  default: 
    std::cerr << "Ignored: " << curr << " (" << (int)curr << ")" << std::endl;
  }
}

for(pos=0;pos<expr.length();pos++){
  const char curr = expr[pos];
  switch(curr){
  case ':': 
    OperatorParse('+');break;
  case '+': 
  case '-':  
  case '*':  
  case '/': 
  case '^': 
    OperatorParse(curr); break;
  case '(': 
    LeftParse(0, pos); break;
  case '{': 
    LeftParse(1, pos); break;
  case '[': 
    LeftParse(2, pos); break;
  case ')': 
  case '}': 
  case ']': 
    RightParse(); break;
  default: 
    std::cerr << "Ignored: " << curr << " (" << (int)curr << ")" << std::endl;
  }
}

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This way you'll know exactly what happens at each moment.

[munna]

I guess this would be more efficient

Thanks for the idea, but can I use

QString(QChar(0xD7)) and (curr==QString(QChar(0xDD)) with switch case ?

Also the I have noticed that there are more than one character that is similar to "-". The user was actually not typing minus but some other similar character.

Thanks a lot

[wysota]

Thanks for the idea, but can I use

QString(QChar(0xD7)) and (curr==QString(QChar(0xDD)) with switch case ?

case 0xd7: case 0xdd: ...

case 0xd7: case 0xdd: ...

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You can also use QChar::unicode() and use unicode values in switch cases.

Also the I have noticed that there are more than one character that is similar to "-". The user was actually not typing minus but some other similar character

Probably – or — These are available as unicode characters, you should either disallow them or convert them to a minus before parsing. The alphabet should be as simple as possible.

[munna]

const char curr = expr[pos];

const char curr = expr[pos];

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gives me the following error

error C2666: 'QString:perator`[]'' : 3 overloads have similar conversions

When I use

const char curr = expr.constref(pos);

const char curr = expr.constref(pos);

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The case 0xdd and 0xd7 doesn't work.

Thanks a lot

[wysota]

So use QChar instead of const char And make a conversion to some int type in the switch so you can make case labels. You have latin1 and unicode conversions available.