问题
I see there is a new class for regular expressions - QRegularExpression. Is it just a typedef for QRegExp, or a new class, or what? And why do we need it, we already have QRegExp?
回答1:
Ok, after some more digging into the docs, I found it really is a new class, it has improvements, but it is only available in Qt5, so you can't use it if you want to compile on both Qt4 and Qt5:
Notes for QRegExp Users
The QRegularExpression class introduced in Qt 5 is a big improvement upon QRegExp, in terms of APIs offered, supported pattern syntax and speed of execution. The biggest difference is that QRegularExpression simply holds a regular expression, and it's not modified when a match is requested. Instead, a QRegularExpressionMatch object is returned, in order to check the result of a match and extract the captured substring. The same applies with global matching and QRegularExpressionMatchIterator.
回答2:
At least for Qt 4.8. I can give a very practical reason to use QRegularExpressions instead of QRegExp:
Do these look dangerous to you?
int index = myQString.indexOf(myQRegExp);
bool okay = myQString.contains(myQRegExp);
Both lines can corrupt your heap, crash or hang your application. I experienced heap corruption and hang with Qt 4.8. The blog post QString::indexOf() versus Qt 4.5 explains that QString::indexOf() modifies a const QRegExp object. QString::contains() inlines QString::indexOf() so it's the same problem.
If you're stuck with Qt4 and thus QRegExp, you could use
int index = myQRegExp.indexIn(myQString);
bool okay = (myQRegExp.indexIn(myQString) != -1);
in your sources instead. Or patch the Qt Sources.
来源：https://stackoverflow.com/questions/29532836/is-there-any-difference-between-qregularexpression-and-qregexp