QString to std:string crash using 3rd party library [Solved]

janfaroe

Hi all. I'm having a funky problem that I don't seem to be able to solve. I'm calling a 3rd party library method with the following signature:

@unsigned char libxbee::Con::Tx(std::string data);@

Calling the method with a string literal poses no problem:

@connection->Tx("Hi there!");@

But since I'm composing a string with values from a database, It surely makes sense to use QString and then convert to std::string:

@std::string str = message.toStdString();
connection->Tx(str);@

However, this makes the 3rd party library code die because of an exception. Printing out the std::str string above shows no trouble at all.

I've tried all sorts of combinations - direct initialization, constructing the std::string from String::toLocal8Bit().data() and other combinations that makes sense to me - but same result.

Why does a literal work and not the QString::toStdString() conversion (or other flavors)? Any workarounds? Suggestions? Please?

hardcodes.de

Have you got the problems only with composed strings from the database?
What happens if you try the same simple string here?

@QString message = QString("Hi there!");
std::string str = message.toStdString();
connection->Tx(str);@

Can you use a std::string on its own? (= passing a string instead of ASCII literal)

@std:string str = std::string("Hi there!");
connection->Tx(str);@

janfaroe

Edit: Was a bit too quick on the keyboard.

Using a std::string argument works just fine.

However, you nailed it with the database content! If I supply a simple "Hi there" QString, the conversion works just as expected.

But - I still don't understand why it fails. My initial suspicion was UTF-8 encoding, but transforming the QString with toLatin1() or toLocal8Bit() doesn't help.

hardcodes.de

I remember boost::filesystem::file_size having problems and crashing on a Mac. I used .toStdWString() then.
Maybe if you enter your database string by hand instead of "Hi there!", like

@QString message = QString("YOURDATABASECONTENT");
std::string str = message.toStdString();
connection->Tx(str);@

I bet it's some "special" character (conversion) or string length. Maybe you can track down the bad character and conclude from there which conversion would be best.

janfaroe

Sorry for not getting back earlier.

I think I have solved the problem - I believe it was related to the state of the unit I was trying to communicate with (needed a reset), combined with the length of the string (the unit buffer is limited). Nothing wrong with the string conversion as suspected at first.

Thanks for your inputs!