通过 for 循环从 C++ 映射中删除元素
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Removing elements from a C++ map through a for-loop
提问by Petter
My STL is a bit rusty, so forgive me for asking a possibly trivial question. Consider the following piece of code:
我的 STL 有点生疏，所以请原谅我提出一个可能微不足道的问题。考虑以下代码：
map<int,int> m;
...
for (auto itr = m.begin(); itr != m.end(); ++itr) {
if (itr->second == 0) {
m.erase(itr);
}
}
The question is: Is it safe to erase elements while looping over the map?
问题是：在遍历地图时擦除元素是否安全？
采纳答案by XAder
I think that you shouldn't use removed iterator at all - in case of lists this causes serious problems, shouldn't be different for maps.
我认为你根本不应该使用删除的迭代器 - 在列表的情况下这会导致严重的问题，地图不应该有所不同。
EDITby Matthieu M: this code is well-formed in C++0x and allowed as an extension by MSVC.
Matthieu M编辑：此代码在 C++0x 中格式良好，并允许作为 MSVC 的扩展。
map<int,int> m;
...
auto itr = m.begin();
while (itr != m.end())
{
if (itr->second == 0) {
itr = m.erase(itr);
}
else
{
itr++;
}
}
回答by Erik
Yes, but not the way you do it. You're invalidating itr when you erase, then incrementing the invalid iterator.
是的，但不是你这样做的方式。您在擦除时使 itr 无效，然后增加无效迭代器。
auto itr = m.begin();
while (itr != m.end()) {
if (itr->first == 0) {
m.erase(itr++);
} else {
++itr;
}
}
回答by decltype
For the example given, It would actually be easier to use the eraseoverload that takes a key as an argument. This function erases all elements in the map with the given key (for a map, this is always either zero or one element)
对于给出的示例，使用将键作为参数的擦除重载实际上会更容易。此函数使用给定的键擦除地图中的所有元素（对于地图，这始终是零或一个元素）
map<int,int> m;
// ...
m.erase(0); // erase all elements with key equivalent to 0
