Re: strange problem with const char *

From:

=?ISO-8859-1?Q?Marcel_M=FCller?= <news.5.maazl@spamgourmet.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 18 Dec 2013 13:02:45 +0100

Message-ID:

<52b18ee5$0$9518$9b4e6d93@newsspool1.arcor-online.net>

Am 18.12.2013 11:28, schrieb alessio211734:

I have problem with conversion from QString to const char * , I know that it's not the right newsgroup but I don't know if is a c++ issue problem.

int main(int argc, char *argv[])
{
     QApplication a(argc, argv);
     QString str("ciao");
     const char * xxx=str.toLatin1().constData();
     _file(str.toLatin1().constData());
     _file(xxx);
     MainWindow w;
     w.show();

     return a.exec();
}

at the first call "_file(str.toLatin1().constData())" the debugger show that the parameter passed to function _file have the correct value while in the last call _file(xxx) the parameters passed to _file function is incorrect. I didn't understand why?

Whatever QString is, read the documentation of QString. Especially the
point how long the storage retuned by constData() remains valid.

Most likely you have undefined behavior because of a dangling reference,
because you passed a temporary to xxx and access it after the QString
instance, that provides the storage has been destroyed.

Marcel