Wrong converting QVariant to double

[estanisgeyer]

Hi,

I have to get a value from a database, for example, 2.3000. Must compare this value with the result of this calculation, as code:

QSqlQuery qry;
...
double y = 2.3;
double x = qry.value(0).toDouble(); // Take 2.30000 in the database, this example;
 
qDebug() << y << x; // Ok, show 2.3 value for x and y;
 
double z = x - y;  // It's result in -2.66454e-15!
 
if (z < 0.00) {
   ...
}
else
{
  ...
}

QSqlQuery qry;
...
double y = 2.3;
double x = qry.value(0).toDouble(); // Take 2.30000 in the database, this example;

qDebug() << y << x; // Ok, show 2.3 value for x and y;

double z = x - y;  // It's result in -2.66454e-15!

if (z < 0.00) {
   ...
}
else
{
  ...
}

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If I make a calculation explicitly declare the values for the variables x and y, result is correct.
I created a method to convert a QString to a double that is working (code below). Any hint to resolve this as I use this function to work around the problem?

QSqlQuery qry;
...
double y = 2.3;
QString sx = qry.value(0).toString();
 
double x = myfunction->toDouble(sx);
double z = x - y;  // It's OK, result 0
...

QSqlQuery qry;
...
double y = 2.3;
QString sx = qry.value(0).toString();

double x = myfunction->toDouble(sx);
double z = x - y;  // It's OK, result 0
...

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Thanks,

Marcelo Estanislau Geyer