C++ Qt foreach 循环排序与 QList 的 for 循环
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Qt foreach loop ordering vs. for loop for QList
提问by Freedom_Ben
When iterating through a QList<T>with a foreachloop, in the tests I conducted the items are returned in the same order as they are with a standard forloop.
当通过迭代QList<T>一个foreach循环，在测试中，我进行了，因为它们与一个标准的项目都以相同的顺序返回for循环。
My question is, will the foreachalways return items in numerical order by index like this, for containers that have natural ordering (like QListand QVector)? For example, are the following alwaysequivalent?
我的问题是，foreach对于具有自然排序（如QList和QVector）的容器，是否总是按这样的索引按数字顺序返回项目？例如，以下是否总是等价的？
QList<T> list;
for( int i=0; i<list.count(); ++i )
{
// process items in numerical order by index
// do something with "list[i]";
}
foreach( T item, list )
{
// will items always be processed in numerical order by index?
// do something with "item";
}
回答by cmannett85
The foreachmacro (aka. Q_FOREACH) uses the begin()and end()iterator request methods of the container.
的foreach宏（又名。Q_FOREACH）使用begin()和end()迭代器请求该容器的方法。
So if your container is a QListor QVectorthen your examples will always be equivalent. You can view the foreachsource code here.
因此，如果您的容器是 a QListorQVector那么您的示例将始终是等效的。您可以在此处查看foreach源代码。
The foreachmacro isn't great though, it makes a copy of the container - so only use on containers that support implicit-sharing. Use C++11 for( : ) {}loops if available, otherwise Boost has an equivalent that is superior.
该foreach宏也不是很大，虽然，它使容器的副本-所以只能在支持共享隐含的容器使用。for( : ) {}如果可用，请使用 C++11循环，否则 Boost 有一个更好的等价物。
