I want check if one of my variables is null

Armin

Hi,
I want check if one of my variables is null
some code will execute .
This is my Code :

if (ui->spinBox->text != &NULL )
{
    {
    ary[counter]=price;
           counter++;
    }
ui->spinBox->clear();
}
}

But i get this error:

error: lvalue required as unary '&' operand
 if (ui->spinBox->text != &NULL )
                           ^

Why?
Thanks.

[Moved to C++ Gurus ~kshegunov]

kshegunov

&NULL means nothing. You can't take the address of a constant, so the compiler is complaining about missing lvalue. Just use the implicit boolean interpretation:

if (ui->spinBox->text)  {
    // It is not null
}

SGaist

Hi,

Because null doesn't have any address. It's not a pointer.

QSpinBox::textreturns a QString. If you want to check if it's null then use QString::isNull.

Armin

Thanks

i use this code:

QString s1 = "" ;

if ((ui->spinBox->text) != s1 )

and still get error

SGaist

Because text is a function. Why not use isNull or isEmpty ?

VRonin

text is a method, not a member, if ((ui->spinBox->text()) != s1 ) yet again, as said above, the correct way would be if (ui->spinBox->text().isEmpty())

Armin

Thanks for all
i solved my problem with this code :

if (ui->spinBox->text().isEmpty())