指向std :: vector和std :: list元素的指针 [英] Pointers to elements of std::vector and std::list

问题描述

我有一个 std :: vector 与一些类 ClassA 的元素。另外，我想使用 std :: map< key，ClassA *> 创建一个索引，它将一些键值映射到向量中包含的元素的指针。

I'm having a std::vector with elements of some class ClassA. Additionally I want to create an index using a std::map<key,ClassA*> which maps some key value to pointers to elements contained in the vector.

当向量末尾添加元素时，有任何保证这些指针保持有效（并指向同一对象）（不是 >插入）。也就是说，以下代码是正确的：

Is there any guarantee that these pointers remain valid (and point to the same object) when elements are added at the end of the vector (not inserted). I.e, would the following code be correct:

std::vector<ClassA> storage;
std::map<int, ClassA*> map;

for (int i=0; i<10000; ++i) {
  storage.push_back(ClassA());
  map.insert(std::make_pair(storage.back().getKey(), &(storage.back()));
}
// map contains only valid pointers to the 'correct' elements of storage

如何使用 std :: list 而不是 std :: vector ？

推荐答案

向量 - 否。由于向量的容量从不缩小，因此即使元素被删除或更改，引用，指针和迭代器仍保持有效，前提是它们引用了操作元素之前的位置。

Vectors - No. Because the capacity of vectors never shrinks, it is guaranteed that references, pointers, and iterators remain valid even when elements are deleted or changed, provided they refer to a position before the manipulated elements. However, insertions may invalidate references, pointers, and iterators.

列表 - 是的，插入和删除元素不会使指针，引用和迭代器无效到其他元素

Lists - Yes, inserting and deleting elements does not invalidate pointers, references, and iterators to other elements

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