overloaded ‘QString(int)’ is ambiguous

The following code fragment gives the compilation error call of overloaded ‘QString(int)’ is ambiguous with qt 4.7.3 (system is linux 64bit, debian unstable)

struct QSAConnection
{
  QSAConnection() : sender(0), signal(0), function_ref() { }
  QSAConnection(QObject *send, const char *sig, QSObject ref)
    : sender(send), signal(Q开发者_如何学编程Latin1String(sig)), function_ref(ref) { }
  QObject *sender;
  QString signal;
  QSObject function_ref;
};

Any tips?

The relevant bit is this line:

QSAConnection() : sender(0), signal(0), function_ref() { }

Since signal is a QString, the signal(0) bit is trying to call a constructor on the QString class that takes an integer as its only parameter. QString has no such constructor according to the Qt documentation. It does however have a constructor taking a char, and a QChar which has an implicit conversion from int. I expect it's ambiguous between those two.

Did you mean this instead?

QSAConnection() : sender(0), signal(), function_ref() { }

Which will default initialize signal. Note that technically it's not necessary to include it in the initializer list at all in that case.

It's a good thing. If it was not ambiguous, you might hit a null-pointer exception on QString::QString(char const* src). This is a common mistake with std::string.