QVector<QString> convert to double

mr__710

Hello everybody,

i have a vector filled with Strings and i want to convert them into double numbers to use them as data points in a graph. The Vector is filled with Strings, because it gets the values from a table.

My current code looks like this:

QVector<double>  x(num_rows);
QVector<QString> y(num_rows);
for (int i=0; i<num_rows; ++i)
{
  x[i] = 1.5*i;
  y[i] = ui->tableWidget->item(i,2)->text().toDouble();
}

The result is:
QVector("%", "\u0000", "\u0000", "\u0000", "\u0000", "\u0000", "%")
instead of:
QVector(37, 36,8, 36,9, 36,7, 36,9, 36,8, 37)

Thanks for your help.

SGaist

Hi and welcome to devnet,

Your y vector looks like that because you made it like a QVector<QString>. Since you already convert your QTableWidget content to double, why not make it a QVector<double> like x ?

mcosta

Hi and welcome to devnet,

y[i] = ui->tableWidget->item(i,2)->text().toDouble();

you're converting a text into number and then assign to a QString!!!

Have you tried with

QVector<double> x(num_rows);
QVector<double> y(num_rows); // <-- Now is a Vector of double
for (int i=0; i<num_rows; ++i)
{
  x[i] = 1.5*i;
  y[i] = ui->tableWidget->item(i,2)->text().toDouble();
}

??

mr__710

it works. Thank you!

One more Question. The values for x[i] are in sql datetime format (yyyy-mm-dd hh:mm:ss). And in my Vector they are converted to Strings. How can i use these data in the right way? My aim is to plot them on xAxis, using QCustomPlot.

QVector<QString>  x(num_rows);
QVector<double> y(num_rows);
for (int i=0; i<num_rows; ++i)
{
  x[i] = ui->tableWidget->item(i,1)->text();
  y[i] = ui->tableWidget->item(i,2)->text().toDouble();
}

response:QVector("2015-11-17 18:50:00",......)

TheBadger

Most Qt SQL drivers return the value as QVariant, from there you can normally use the QVariant::toDate() or QVariant::toDateTime() functions.

Otherwise you need to use the static QDateTime::fromString() function, just set the format correctly.

QDateTime date = QDateTime::fromString(x[i], "yyyy-MM-dd hh:mm:ss");

PS: the above format is just an example, you need to update based on your format that you have but it looks like it should work based on your response:

response:QVector("2015-11-17 18:50:00",......)

mr__710

I got it, thank you!