C++'s string (and other C++ stl classes) has clear() and empty() all only change the string's size to 0, not change the string's capacity and not free the memory.

but qt's QString::clear() will change the capacity and free the memory as below:

inline void QString::clear(){ if (!isNull()) *this = QString(); }

this is not efficient when use the same QString many times, so QString::clear() better be the same with the C++'s string.

thanks!