How can I convert a QString to char* and vice versa ?

In order to convert a QString to a char*, then you first need to get a latin1 representation of the string by calling toLatin1() on it which will return a QByteArray. Then call data() on the QByteArray to get a pointer to the data stored in the byte array. See the documentation:

http://doc.trolltech.com/4.2/qstring.html#toLatin1

http://doc.trolltech.com/4.2/qbytearray.html#data

See the following example for a demonstration:

int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    QString str1 = "Test";
    QByteArray ba = str1.toLatin1();
    const char *c_str2 = ba.data(); 
    printf("str2: %s", c_str2);
    return app.exec();    
}

Note that it is necessary to store the bytearray before you call data() on it, a call like the following

const char *c_str2 = str2.toLatin1().data();

will make the application crash as the QByteArray has not been stored and hence no longer exists

To convert a char* to a QString you can use the QString constructor that takes a QLatin1String, e.g:

QString string = QString(QLatin1String(c_str2)) ;

See the documentation:

http://doc.trolltech.com/4.2/qlatin1string.html