string str;
QString qstr;
//从QString 到 std::string
str = qstr.toStdString();
//从std::string 到QString
qstr = QString::fromStdString(str);
-------------------------------------------------------------
std::string cstr;
QString qstring;
//从std::string 到QString
qstring = QString(QString::fromLocal8Bit(cstr.c_str()));
//从QString 到 std::string
cstr = string((const char *)qstring.toLocal8Bit());
https://blog.csdn.net/hellokandy/article/details/55254071