![Check If a Std: :Vector Contains a Certain Object? [Duplicate]](https://docuprint.cloud68.co/uploads/check-if-a-std-vector-contains-a_1200.jpg)
Is there something in <algorithm> which allows you to check if a std:: container contains something? Or, a way to make one, for example:
if(a.x == b.x && a.y == b.y)
return true;
return false;
Can this only be done with std::map since it uses keys?
Thanks
3 Answers
Checking if v contains the element x:
#include <algorithm>
if(std::find(v.begin(), v.end(), x) != v.end()) {
/* v contains x */
} else {
/* v does not contain x */
}
Checking if v contains elements (is non-empty):
if(!v.empty()){
/* v is non-empty */
} else {
/* v is empty */
}
If searching for an element is important, I'd recommend std::set instead of std::vector. Using this:
std::find(vec.begin(), vec.end(), x) runs in O(n) time, but std::set has 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::set also guarantees all the added elements are unique, which saves you from having to do anything like if not contained then push_back()....
See question: How to find an item in a std::vector?
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.
