The use of containers in Qt brings great convenience to C++ development, and some member functions extended by containers such as QVector and QMap are also very convenient. But how efficient are Qt's containers compared with STL's? I've just written a few simple traversal examples to test the more efficient methods of containers like QVector and vector.
Test environment:
System: windows 10
Compiler: MingGW mingw5.3.0
Qt version: 5.9.7
Hardware: i7 8, 16G memory
I. Testing various traversal methods of QVector and vector:
void CompareQVectorAndVectorTraverse()
{
int size = 100000000;
QVector<int> qv(size, 1);
vector<int> v(size, 1);
printf("vector size: %d\n", size);
// const_iterator comparison
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 comparison
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);
//[comparison]
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() comparison
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);
//Comparison
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);
}
Operation results:
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
2. Testing various traversal methods of QMap and map:
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 comparison
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 comparison
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);
}Operation results:
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
The results are basically the same as expected. The result is that QVector is best used for (T&t: qvT) mode. QMap uses iterator faster, and const_iterator is similar to iterator.