Is there any ways to check for nan inf and -inf in Qt?

[aarelovich]

Hi:

Simple question for today. Does Qt provide any function, macro or something that checks if a qreal has a value of Inf -Inf or nan?

I know c++ has a way using certain libraries, but I thought Qt might have something like this too.

If there is I can't find it anywhere?

Thanks

[Boron]

No.
qreal is just a simple typedef double qreal (float on ARM architecture).
So you can handle it as if it is a double/float.

[aarelovich]

I did.

I've just thought that since there were functions like qBound qAbs, qMax there would be something to detect the nans and Ifs.

Thanks

[Boron]

Unfortunately not. It has to be done the usual way (whatever that might be; I'm avoiding floating point arithmetic deliberately).

[aarelovich]

To check for NaN is relatively easy as it is the only case where

value == value is false.

To check for Inifinity, seeing as it is a sort of "valid value" is a bit more complex and requires the use of the <limits> c++ library. Here is the code:

QString Approximator::ValidQReal(qreal value){
    if (value != value){
        return "NaN";
    }
    else if (value > std::numeric_limits<qreal>::max()){
        return "+Inf";
    }
    else if (value < -std::numeric_limits<qreal>::max()){
        return "-Inf";
    }
    else
        return "";
}

QString Approximator::ValidQReal(qreal value){
    if (value != value){
        return "NaN";
    }
    else if (value > std::numeric_limits<qreal>::max()){
        return "+Inf";
    }
    else if (value < -std::numeric_limits<qreal>::max()){
        return "-Inf";
    }
    else
        return "";
}

To copy to clipboard, switch view to plain text mode 

In my particular case I return a QString that eventually cuts my thread and shows an errro message of what was found.

[AndyArmitage]

Of course this thread is quite old, but these are now available: qIsInf(), qIsNan(), qIsFinite.
I followed the above advice before a colleague pointed out that this is now available, at least in Qt5.4