Qt QVector和vector以及QMap和map的遍历性能对比

　　使用Qt中的容器给C++开发带来很大的便利，而且QVector和QMap等容器扩展的一些成员函数也是很方便的。但是Qt的这些容器和STL库的容器比，效率到底怎么样？我就写了几个简单的遍历的例子，测试了QVector、vector等容器的那些方法效率更高。

测试环境：

系统：windows 10

编译器：MingGW mingw5.3.0

Qt版本：5.9.7

硬件：i7 8代，16G内存

一. 测试QVector和vector的各种遍历的方法：

1 void CpareQVectorAndVectorTraverse() 2 16 qint64 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 17 printf( "qvector ConstIterator %dms\n", end start ); 18 printf("%d\n", sum); 19 20 QVector<int>::const_iterator cqvit2; 21 sum = 0; 22 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 23 for( cqvit2 = qvbegin(); cqvit2 != qvend(); ++cqvit2) 24 27 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 28 printf( "qvector const_iterator %dms\n", end start ); 29 printf("%d\n", sum); 30 31 vector<int>::const_iterator cvit; 32 sum = 0; 33 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 34 for( cvit = vbegin(); cvit != vend(); ++cvit ) 35 38 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 39 printf( "stl vector const_iterator %dms\n", end start ); 40 printf("%d\n", sum); 41 42 // iterator比较 43 QVector<int>::iterator it; 44 sum = 0; 45 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 46 for( it = qv.begin(); it != qv.end(); ++it) 47 50 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 51 printf( "qvector iterator %dms\n", end start ); 52 printf("%d\n", sum); 53 54 vector<int>::iterator vit; 55 sum = 0; 56 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 57 for( vit = v.begin(); vit != v.end(); ++vit ) 58 61 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 62 printf( "stl vector iterator %dms\n", end start ); printf("%d\n", sum); 64 65 //[]比较 66 sum = 0; 67 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 68 for( int i = 0; i < qv.size(); ++i) 69 72 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 73 printf( "QVector [] %dms\n", end start ); 74 printf("%d\n", sum); 75 76 77 sum = 0; 78 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 79 for( int i = 0; i < v.size(); ++i) 80 83 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 84 printf( "stl vector [] %dms\n", end start ); 85 printf("%d\n", sum); 86 87 //.data()比较 88 sum = 0; 89 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 90 int *data = qv.data(); 91 for( int i = 0; i < qv.size(); ++i) 92 95 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 96 printf( "QVector .data() %dms\n", end start ); 97 printf("%d\n", sum); 98 99 sum = 0; 100 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 101 data = v.data(); 102 for( int i = 0; i < v.size(); ++i) 103 106 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 107 printf( "stl vector .data() %dms\n", end start ); 108 printf("%d\n", sum); 109 110 //：比较 111 sum = 0; 112 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 113 for( int val : qv ) 114 117 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 118 printf( "QVector : %dms\n", end start ); 119 printf("%d\n", sum); 120 121 sum = 0; 122 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 123 for( int val : v) 124 127 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 128 printf( "stl vector : %dms\n", end start ); 129 printf("%d\n", sum); 130 }

运行结果：

1 vector size: 100000000 2 qvector ConstIterator 1252ms 3 100000000 4 qvector const_iterator 1254ms 5 100000000 6 stl vector const_iterator 1318ms 7 100000000 8 qvector iterator 4233ms 9 100000000 10 stl vector iterator 1319ms 11 100000000 12 QVector [] 4862ms 13 100000000 14 stl vector [] 456ms 15 100000000 16 QVector .data() 275ms 17 100000000 18 stl vector .data() 296ms 19 100000000 20 QVector : 187ms 21 100000000 22 stl vector : 870ms 23 100000000

二.测试QMap和map的各种遍历的方法：

1 void CpareQMapAndMapTraverse() 2 13 QMap<string, int> qm(m); 14 printf("map size: %d\n", m.size()); 15 16 17 //iterator比较 18 QMap<string, int>::iterator qmit; 19 sum = 0; 20 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 21 for(qmit = qm.begin(); qmit != qm.end(); ++qmit ) 22 25 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 26 printf( "QMap iterator %dms\n", end start ); 27 printf("%d\n", sum); 28 29 map<string, int>::iterator mit; 30 sum = 0; 31 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 32 for( mit = m.begin(); mit != m.end(); ++mit ) 33 36 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 37 printf( "stl::map iterator %dms\n", end start ); 38 printf("%d\n", sum); 39 40 //const_iterator比较 41 QMap<string, int>::const_iterator cqmit; 42 sum = 0; 43 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 44 for(cqmit = qmbegin(); cqmit != qmend(); ++cqmit ) 45 48 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 49 printf( "QMap const_iterator %dms\n", end start ); 50 printf("%d\n", sum); 51 52 map<string, int>::const_iterator cmit; 53 sum = 0; 54 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 55 for( cmit = mbegin(); cmit != mend(); ++cmit ) 56 59 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 60 printf( "stl::map const_iterator %dms\n", end start ); 61 printf("%d\n", sum); 62 QMap<string, int>::key_iterator qmkeyit; 64 sum = 0; 65 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 66 for( qmkeyit = qm.keyBegin(); qmkeyit != qm.keyEnd(); ++qmkeyit ) 67 70 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 71 printf( "QMap key_iterator %dms\n", end start ); 72 printf("%d\n", sum); 73 74 sum = 0; 75 start = QDateTime::currentDateTime().toMSecsSinceEpoch(); 76 for( string k : qm.keys() ) 77 80 end = QDateTime::currentDateTime().toMSecsSinceEpoch(); 81 printf( "QMap .keys %dms\n", end start ); 82 printf("%d\n", sum); 83 84 }

运行结果：

1 map size: 1000000 2 QMap iterator 49ms 3 1783293664 4 stl::map iterator 38ms 5 1783293664 6 QMap const_iterator 33ms 7 1783293664 8 stl::map const_iterator 38ms 9 1783293664 10 QMap key_iterator 407ms 11 1783293664 12 QMap .keys 551ms 13 1783293664

基本和预期的结果差不多，得出结果是QVector最好用for(T &t : qvT)方式。QMap用iterator比较快，而且const_iterator和iterator差不多。

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