I'm new to Qt and trying to learn the idioms.
Qt automatically takes a copy of the container when it enters a foreach loop. If you modify the container as you are iterating, that won't affect the loop.
But it doesn't say how to remove an element while iterating with foreach. My best guess is something like:
int idx = 0;
foreach (const Foo &foo, fooList) {
if (bad(foo)) {
fooList.removeAt(idx);
}
++idx;
}
Seems ugly to have to scope idx outside the loop (and to have to maintain a separate loop counter at all).
Also, I know that foreach makes a copy of the QList, which is cheap, but what happens once I remove an element -- is that still cheap or is there an expensive copy-on-modify going on? Yes, deep copy happens.
EDIT : This doesn't seem like idiomatic Qt either.
for (int idx = 0; idx < fooList.size(); ) {
const Foo &foo = fooList[idx];
if (bad(foo)) {
fooList.removeAt(idx);
}
else ++idx;
}
解决方案
You should better use iterators for that:
// Remove all odd numbers from a QList
QMutableListIterator i(list);
while (i.hasNext()) {
if (i.next() % 2 != 0)
i.remove();
}
