C++ 检查 std::vector 是否包含某个对象？
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check if a std::vector contains a certain object?
提问by jmasterx
Is there something in <algorithm>which allows you to check if a std:: container contains something? Or, a way to make one, for example:
有什么东西<algorithm>可以让您检查 std:: 容器是否包含某些东西？或者，一种制作方法，例如：
if(a.x == b.x && a.y == b.y)
return true;
return false;
Can this only be done with std::mapsince it uses keys?
std::map因为它使用密钥，所以只能这样做吗？
Thanks
谢谢
回答by You
Checking if vcontains the element x:
检查是否v包含元素x：
#include <algorithm>
if(std::find(v.begin(), v.end(), x) != v.end()) {
/* v contains x */
} else {
/* v does not contain x */
}
Checking if vcontains elements (is non-empty):
检查是否v包含元素（非空）：
if(!v.empty()){
/* v is non-empty */
} else {
/* v is empty */
}
回答by AshleysBrain
If searching for an element is important, I'd recommend std::setinstead of std::vector. Using this:
如果搜索元素很重要，我会推荐std::set而不是std::vector. 使用这个：
std::find(vec.begin(), vec.end(), x)runs in O(n) time, but std::sethas its own find()member (ie. myset.find(x)) which runs in O(log n) time - that's much more efficient with large numbers of elements
std::find(vec.begin(), vec.end(), x)在 O(n) 时间内运行，但std::set有自己的find()成员（即myset.find(x)），它在 O(log n) 时间内运行 - 对于大量元素来说效率更高
std::setalso guarantees all the added elements are unique, which saves you from having to do anything like if not contained then push_back()....
std::set还保证所有添加的元素都是唯一的，这样您就不必执行诸如if not contained then push_back()....
回答by NeilDurant
See question: How to find an item in a std::vector?
请参阅问题：如何在 std::vector 中查找项目？
You'll also need to ensure you've implemented a suitable operator==()for your object, if the default one isn't sufficient for a "deep" equality test.
您还需要确保您已经实现了一个适合operator==()您的对象，如果默认一个不足以进行“深度”相等测试。
