C++ 计算代码块运算时间

using namespace std::chrono;
int t1 = 0;
const auto before = steady_clock::now();
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t1 += duration_cast(steady_clock::now() - before).count();
qDebug() << t1 / 1000 << "(ms)";

const QTime startTime = QTime::currentTime();
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const QTime stopTime = QTime::currentTime();
QDebug(QtMsgType::QtDebugMsg) << startTime.msecsTo(stopTime) << "ms";