check if a std::vector contains a certain object?

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.