A strange problem with QList and QVector

HFT_developer

Hi,

I am coming across a strange issue where my aim is to convert a QList<double> to std::vector<double>. This is to test a C++ code which I am trying to integrate with a Qt based GUI, altho I don't like this conversion as it it quite inefficient. Right now this is for testing purposes.

Anyways:

This is the problem:

    QVector<double> _temp1 =m_numerator.toVector();
    QVector<double> _temp2 =m_denominator.toVector();
    std::vector<double> _temp11 = _temp1.toStdVector();//  No member named 'toStdVector' in List<double>'
    std::vector<double> _temp21 = _temp2.toStdVector();// No member named 'toStdVector' in List<double>'

mpergand

@HFT_developer
There's something wrong somewhere, because _tempX are QVectors not QLists !
Try to clean/rebuild your project.

I tried this with no issue:

QList<double> l={1,22,-1,.5};
QVector<double> _temp1 =l.toVector();
std::vector<double> _temp11 = _temp1.toStdVector();

Chris Kawa

This would work in Qt5 but not Qt6.

QVector and QList were unified in Qt6 and QVector is now just an alias for QList, so the message is a bit misleading but correct - there's no direct conversion to std vector.

In Qt6 you can convert it like this:

std::vector<double> _temp11 {_temp1.begin(), _temp1.end()};

Btw. if you want to avoid the copy maybe you could use std::span on the non-Qt side of the code? It's a wrapper over external data and you can use it just like a vector, but it doesn't copy the elements. You would create it very cheaply like this:

std::span<double> _temp11 {_temp1};