c – 为什么在隐式共享容器上使用迭代器时首先要进行复制？

Thanks to implicit sharing,it is very inexpensive for a function to return a container per value. The Qt API contains dozens of functions that return a QList or QStringList per value (e.g.,QSplitter::sizes()). If you want to iterate over these using an STL iterator,you should always take a copy of the container and iterate over the copy. For example:

// RIGHT
const QList<int> sizes = splitter->sizes();
QList<int>::const_iterator i;
for (i = sizes.begin(); i != sizes.end(); ++i)
    ...

// WRONG
QList<int>::const_iterator i;
for (i = splitter->sizes().begin();
        i != splitter->sizes().end(); ++i)
    ...

如果应用“错误”方法会发生什么？