I just created a qstring from a double, but I misplaced the parenthesis. It did compile and the QString was fine in my computer, but the string had a lot of added garbage data data in front of the "1500 m" string I was producing in my friends computer.

My question is: What is actually going on in this codeline. Why doesn't it produce a compiler error?

double distance = 1500;
QString distanceString = QString("%1 m").arg(QString::number(distance), 'f', 1);

No compiler errors, and different behaviour on different computers.

CodePudding user response：

QString("%1 m").arg(QString::number(distance), 'f', 1) is calling the 3-argument overload QString::arg(const QString &a, int fieldWidth, QChar fillChar)

So in this case, your parameters will go through implicit conversions:

• 'f' converts to int, which is 102
• 1 converts to char and which ends up being the SOH ASCII character

Becuase these conversions are allowed to happen implicitly, the call to arg is well-formed and so this is not a compile error.

The function then will do what is designed to do and replace "%1" with your number, but padded to a length of 102, padded with the unprintable SOH character. So you end up with a strange looking output.