一、性能测试

最近使用opengl画点云数据时发现比较卡顿，原因是我使用了QList数据结构，后面改为QVector改善很多，速度提升1倍。

private:
    QVector<QVector3D> m_pointVector;

void PointCloud3dWidget::drawGL()
{
    drawGrid();
    drawCoordinates();
    glBegin(GL_POINTS);
    foreach (auto vec3d, m_pointVector)
    {
        glVertex3d(vec3d.x(), vec3d.y(), vec3d.z());
    }
    glEnd();
}

为了探寻哪种数据结构、哪种遍历方式最快，我对QList与QVector分别用小数据量，中数据量，大数据量进行了测试，并且使用了for、foreach、auto、迭代器组合了7种遍历方式做了对比，测试结果如下：

测试代码如下：

void QListTest(QList<QVector3D> &pointList)
{
    qDebug() << "=======QList<QVector3D>======";
    QTime ms;
    ms.start();

    /* 方式1：foreach , */
    foreach (QVector3D vec, pointList)
    {
        int x = vec.x();
        int y = vec.y();
        int z = vec.z();
    }
    qDebug() << "foreach ," << ms.elapsed() << "ms";

    /* 方式2：foreach auto , */
    ms.restart();
    foreach (auto vec, pointList)
    {
        int x = vec.x();
        int y = vec.y();
        int z = vec.z();
    }
    qDebug() << "foreach auto ," << ms.elapsed() << "ms";

    /* 方式3：for ;  ;*/
    ms.restart();
    for(int i = 0; i < pointList.size() ; ++i)
    {
        QVector3D vec = pointList.at(i);
        int x = vec.x();
        int y = vec.y();
        int z = vec.z();
    }
    qDebug() << "for ;" << ms.elapsed() << "ms";

    /* 方式4：for : */
    ms.restart();
    for(QVector3D vec : pointList)
    {
        int x = vec.x();
        int y = vec.y();
        int z = vec.z();
    }
    qDebug() << "for :" << ms.elapsed() << "ms";

    /* 方式5：for auto : */
    ms.restart();
    for(auto vec : pointList)
    {
        int x = vec.x();
        int y = vec.y();
        int z = vec.z();
    }
    qDebug() << "for auto :" << ms.elapsed() << "ms";

    /* 方式6：for iterator */
    ms.restart();
    QList<QVector3D>::iterator iter;
    for (iter = pointList.begin(); iter != pointList.end(); iter++)
    {
        int x = (*iter).x();
        int y = (*iter).y();
        int z = (*iter).z();
    }
    qDebug() << "iterator" << ms.elapsed() << "ms";

    /* 方式7：for auto iterator  */
    ms.restart();
    for (auto iter = pointList.begin(); iter != pointList.end(); iter++)
    {
        int x = (*iter).x();
        int y = (*iter).y();
        int z = (*iter).z();
    }
    qDebug() << "iterator auto" << ms.elapsed() << "ms";
}

void QVectorTest(QVector<QVector3D> &pointVector)
{
    qDebug() << "=======QVector<QVector3D>======";
    QTime ms;
    ms.start();
    /* 方式1：foreach , */
    foreach (QVector3D vec, pointVector)
    {
        int x = vec.x();
        int y = vec.y();
        int z = vec.z();
    }
    qDebug() << "foreach" << ms.elapsed() << "ms";

    /* 方式2：foreach auto , */
    ms.restart();
    foreach (auto vec, pointVector)
    {
        int x = vec.x();
        int y = vec.y();
        int z = vec.z();
    }
    qDebug() << "foreach auto" << ms.elapsed() << "ms";

    /* 方式3：for ;  ;*/
    ms.restart();
    for(int i = 0; i < pointVector.size() ; ++i)
    {
        QVector3D vec = pointVector.at(i);
        int x = vec.x();
        int y = vec.y();
        int z = vec.z();
    }
    qDebug() << "for ;" << ms.elapsed() << "ms";

    /* 方式4：for : */
    ms.restart();
    for(QVector3D vec : pointVector)
    {
        int x = vec.x();
        int y = vec.y();
        int z = vec.z();
    }
    qDebug() << "for :" << ms.elapsed() << "ms";

    /* 方式5：for auto : */
    ms.restart();
    for(auto vec : pointVector)
    {
        int x = vec.x();
        int y = vec.y();
        int z = vec.z();
    }
    qDebug() << "for auto :" << ms.elapsed() << "ms";

    /* 方式6：for iterator*/
    ms.restart();
    QVector<QVector3D>::iterator iter;
    for (iter = pointVector.begin(); iter != pointVector.end(); iter++)
    {
        int x = (*iter).x();
        int y = (*iter).y();
        int z = (*iter).z();
    }
    qDebug() << "iterator" << ms.elapsed() << "ms";

    /* 方式7：for auto iterator  */
    ms.restart();
    for (auto iter = pointVector.begin(); iter != pointVector.end(); iter++)
    {
        int x = (*iter).x();
        int y = (*iter).y();
        int z = (*iter).z();
    }
    qDebug() << "iterator auto" << ms.elapsed() << "ms";
}

int main()
{
    QList<QVector3D> pointList;
    QVector<QVector3D> pointVector;
    for(int i = 0; i < 300; ++i)
    {
        for(int j = 0; j < 300; ++j)
        {
            pointList.append(QVector3D(i, j, i + j));
            pointVector.append(QVector3D(i, j, i + j));
        }
    }
    QListTest(pointList);
    QVectorTest(pointVector);

    return 0;
}