Debugging QT project found an error, error opening device.
Look at the error and think it’s a hardware problem. Look for this character.

It must have loaded the dynamic library, and the error was printed in the dynamic library.
Deubg step by step found that it was qjson parsing error, Nari???
What is the relationship between qjson parsing and opening device errors?

Then use:

ll@ubuntu:~/QJson/lib$ strings libqjson.so | grep opening

It is found that there is this:
error opening device

Finally, look at the GitHub source code:
https://github.com/flavio/qjson/blob/master/src/parser.cpp

QVariant Parser::parse(QIODevice* io, bool* ok)
{
  d->reset();

  if (!io->isOpen()) {
    if (!io->open(QIODevice::ReadOnly)) {
      if (ok != 0)
        *ok = false;
      qCritical ("Error opening device");
      return QVariant();
    }
  }
  ......
}
 

I think it should be changed to error opening file.
all is file!
That’s all.