ask    QString::lastIndexOf [复制链接]

关于Qstring的lastIndexOf的含义
int QString::lastIndexOf ( const QString & str, int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const
如下列 from =6 or 5的执行结果如何解释
QString x = "crazy azimuths";
    QString y = "az";
    x.lastIndexOf(y);           // returns 6
   x.lastIndexOf(y, 6);        // returns 6？？
    x.lastIndexOf(y, 5);        // returns 2？？
    x.lastIndexOf(y, 1);        // returns -1