我注意到在有效的STL
向量是这样一种序列 默认情况下应该使用。
这是什么意思?似乎忽略效率向量可以做任何事情。
谁能给我一个场景,其中向量不是一个可行的选择,但必须使用列表?
我注意到在有效的STL
向量是这样一种序列 默认情况下应该使用。
这是什么意思?似乎忽略效率向量可以做任何事情。
谁能给我一个场景,其中向量不是一个可行的选择,但必须使用列表?
当前回答
任何时候都不能使迭代器失效。
其他回答
在表格中总结答案以供快速参考:
Vector | List | |
---|---|---|
Access | Faster | Slower |
Insert/Delete Operations | Slower | Faster |
Memory Allocation | Contiguous | Non-contiguous |
Size Pre-allocation | Need to be reserved | Not necessary to reserve |
Space Required Per Element | Only for the element itself | For element and pointers to next (and optionally previous elements) |
任何时候都不能使迭代器失效。
std::list的一个特殊功能是拼接(将列表的一部分或整个链接或移动到另一个列表中)。
或者如果你的内容复制非常昂贵。在这种情况下,使用列表对集合进行排序可能更便宜。
还要注意,如果集合很小(并且复制内容的开销不是特别大),即使在任何地方插入和删除,vector的性能也可能优于list。列表单独分配每个节点,这可能比移动几个简单的对象要昂贵得多。
我不认为有什么严格的规定。这取决于您最想对容器做什么,以及您希望容器有多大以及所包含的类型。vector通常优于list,因为它将其内容分配为单个连续块(它基本上是一个动态分配的数组,在大多数情况下,数组是保存一堆东西的最有效方式)。
想要重复将大量项插入序列末尾以外的任何位置的情况。
看看每种不同类型的容器的复杂度保证:
标准容器的复杂性保证是什么?
在向量和列表的情况下,对我来说,主要的区别如下:
向量
A vector stores its elements in contiguous memory. Therefore, random access is possible inside a vector which means that accessing an element of a vector is very fast because we can simply multiply the base address with the item index to access that element. In fact, it takes only O(1) or constant time for this purpose. Since a vector basically wraps an array, every time you insert an element into the vector (dynamic array), it has to resize itself by finding a new contiguous block of memory to accommodate the new elements which is time-costly. It does not consume extra memory to store any pointers to other elements within it.
list
A list stores its elements in non-contiguous memory. Therefore, random access is not possible inside a list which means that to access its elements we have to use the pointers and traverse the list which is slower relative to vector. This takes O(n) or linear time which is slower than O(1). Since a list uses non-contiguous memory, the time taken to insert an element inside a list is a lot more efficient than in the case of its vector counterpart because reallocation of memory is avoided. It consumes extra memory to store pointers to the element before and after a particular element.
因此,记住这些区别,我们通常会考虑内存、频繁的随机访问和插入来决定给定场景中向量和列表的胜者。