qt中QVector和vector以及QMap和map的遍歷性能對比

使用Qt中的容器給C++開發帶來很大的便利，而且QVector和QMap等容器擴展的一些成員函數也是很方便的。但是Qt的這些容器和STL庫的容器比，效率到底怎麼樣？我就寫了幾個簡單的遍歷的例子，測試了QVector、vector等容器的那些方法效率更高。

測試環境：

系統：windows 10

編譯器：MingGW mingw5.3.0

Qt版本：5.9.7

硬件：i7 8代，16G內存

一. 測試QVector和vector的各種遍歷的方法：

void CompareQVectorAndVectorTraverse()
{
    int size = 100000000;
    QVector<int> qv(size, 1);
    vector<int> v(size, 1);

    printf("vector size: %d\n", size);
// const_iterator比較
    QVector<int>::ConstIterator cqvit;
    int sum = 0;
    qint64 start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( cqvit = qv.constBegin(); cqvit != qv.constEnd(); ++cqvit)
    {
        sum += *cqvit;
    }
    qint64 end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "qvector ConstIterator %dms\n", end - start );
    printf("%d\n", sum);

    QVector<int>::const_iterator cqvit2;
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( cqvit2 = qv.cbegin(); cqvit2 != qv.cend(); ++cqvit2)
    {
        sum += *cqvit2;
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "qvector const_iterator %dms\n", end - start );
    printf("%d\n", sum);

    vector<int>::const_iterator cvit;
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( cvit = v.cbegin(); cvit != v.cend(); ++cvit )
    {
        sum += *cvit;
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "stl vector const_iterator %dms\n", end - start );
    printf("%d\n", sum);

// iterator比較
    QVector<int>::iterator it;
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( it = qv.begin(); it != qv.end(); ++it)
    {
        sum += *it;
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "qvector iterator %dms\n", end - start );
    printf("%d\n", sum);

    vector<int>::iterator vit;
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( vit = v.begin(); vit != v.end(); ++vit )
    {
        sum += *vit;
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "stl vector iterator %dms\n", end - start );
    printf("%d\n", sum);

//[]比較
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( int i = 0; i < qv.size(); ++i)
    {
        sum += qv[i];
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "QVector [] %dms\n", end - start );
    printf("%d\n", sum);


    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( int i = 0; i < v.size(); ++i)
    {
        sum += v[i];
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "stl vector [] %dms\n", end - start );
    printf("%d\n", sum);

//.data()比較
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    int *data = qv.data();
    for( int i = 0; i < qv.size(); ++i)
    {
        sum += data[i];
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "QVector .data() %dms\n", end - start );
    printf("%d\n", sum);

    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    data = v.data();
    for( int i = 0; i < v.size(); ++i)
    {
        sum += data[i];
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "stl vector .data() %dms\n", end - start );
    printf("%d\n", sum);

//：比較
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( int val : qv )
    {
        sum += val;
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "QVector : %dms\n", end - start );
    printf("%d\n", sum);

    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( int val : v)
    {
        sum += val;
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "stl vector : %dms\n", end - start );
    printf("%d\n", sum);
}

運行結果：

vector size: 100000000
qvector ConstIterator 1252ms
100000000
qvector const_iterator 1254ms
100000000
stl vector const_iterator 1318ms
100000000
qvector iterator 4233ms
100000000
stl vector iterator 1319ms
100000000
QVector [] 4862ms
100000000
stl vector [] 456ms
100000000
QVector .data() 275ms
100000000
stl vector .data() 296ms
100000000
QVector : 187ms
100000000
stl vector : 870ms
100000000

二. 測試QMap和map的各種遍歷的方法：

void CompareQMapAndMapTraverse()
{
    int size = 1000000;
    qint64 sum = 0;
    qint64 start, end;
    map<string, int> m;
    char *tmps = new char[10];
    for( int i = 0; i < size; ++i )
    {
        sprintf( tmps, "%s%d", "a", i);
        m.insert( make_pair(tmps, i) );
    }
    QMap<string, int> qm(m);
    printf("map size: %d\n", m.size());


//iterator比較
    QMap<string, int>::iterator qmit;
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for(qmit = qm.begin(); qmit != qm.end(); ++qmit )
    {
        sum += qmit.value();
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "QMap iterator %dms\n", end - start );
    printf("%d\n", sum);

    map<string, int>::iterator mit;
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( mit = m.begin(); mit != m.end(); ++mit )
    {
        sum += mit->second;
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "stl::map iterator %dms\n", end - start );
    printf("%d\n", sum);

//const_iterator比較
    QMap<string, int>::const_iterator cqmit;
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for(cqmit = qm.cbegin(); cqmit != qm.cend(); ++cqmit )
    {
        sum += cqmit.value();
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "QMap const_iterator %dms\n", end - start );
    printf("%d\n", sum);

    map<string, int>::const_iterator cmit;
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( cmit = m.cbegin(); cmit != m.cend(); ++cmit )
    {
        sum += cmit->second;
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "stl::map const_iterator %dms\n", end - start );
    printf("%d\n", sum);

    QMap<string, int>::key_iterator qmkeyit;
    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( qmkeyit = qm.keyBegin(); qmkeyit != qm.keyEnd(); ++qmkeyit )
    {
        sum += qm[*qmkeyit];
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "QMap key_iterator %dms\n", end - start );
    printf("%d\n", sum);

    sum = 0;
    start = QDateTime::currentDateTime().toMSecsSinceEpoch();
    for( string k : qm.keys() )
    {
        sum += qm[k];
    }
    end = QDateTime::currentDateTime().toMSecsSinceEpoch();
    printf( "QMap .keys %dms\n", end - start );
    printf("%d\n", sum);

}

運行結果：

map size: 1000000
QMap iterator 49ms
1783293664
stl::map iterator 38ms
1783293664
QMap const_iterator 33ms
1783293664
stl::map const_iterator 38ms
1783293664
QMap key_iterator 407ms
1783293664
QMap .keys 551ms
1783293664

基本和預期的結果差不多，得出結果是QVector最好用for(T &t : qvT)方式。QMap用iterator比較快，而且const_iterator和iterator差不多。