Check out example codes for "c++ sort vector of objects by property". It will help you in understanding the concepts better.

Code Example 1

class cat {
public:
    int age;
    bool operator< (const cat &other) const {
        return age < other.age;
    }
};

Code Example 2

vector< cat > catSorter::SortCatsByAge(){
   vector< cat > cats_copy = cats;
   std::sort(cats_copy.begin(), cats_copy.end());
   return cats_copy;
}

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