Solved Is there principal difference between QRegularExpression and QRegExp?
You should use QRegularExpression
Note: In Qt 5, the new QRegularExpression class provides a Perl compatible implementation of regular expressions and is recommended in place of QRegExp.
So i guess the biggest difference is its compatibility
QRegExp is a custom regular expression implementation.
QRegularExpression uses PCRE as a backend.
Also, QRegExp should be considered deprecated and not used in new code.