The objects in the std::set are stored as const StudentT. So when you try to call getId() with the const object the compiler detects a problem, mainly you’re calling a non-const member function on const object which is not allowed because non-const member functions make NO PROMISE not to modify the object; so the compiler … Read more
You can do something like: std::set<int> s1; std::set<int> s2; // fill your sets s1.insert(s2.begin(), s2.end());
I decided to ask Alexander Stepanov (designer of the STL) about this. I’m allowed to quote him as follows: Originally, I proposed 3-way comparisons. The standard committee asked me to change to standard comparison operators. I did what I was told. I have been advocating adding 3-way components to the standard for over 20 years. … Read more
In practice, not much. If you’re inserting a large number of already in order elements into an empty set, the second will be somewhat faster, but that’s about it. std::insert_iterator calls insert with the iterator; std::set interprets it as a hint, and inserts in constant time (rather than lg n) if the insertion is immediately … Read more
STL has no built in thread support, so you’ll have to extend the STL code with your own synchronization mechanisms to use STL in a multithreaded environment. For example look here: link text Since set is a container class MSDN has following to say about the thread safety of the containers. A single object is … Read more
A set is like a map with no values, only keys. Since those keys are used for a tree that accelerates operations on the set, they cannot change. Thus all elements must be const to keep the constraints of the underlying tree from being broken.
Both std::set and std::map are associative containers. The difference is that std::sets contain only the key, while in std::map there is an associated value. Choosing one over the other depends mainly on what the task at hand is. If you want to build a dictionary of all the words that appear in a text, you … Read more
What comparator are you using? For the default this will work: if(!myset.empty()) *myset.rbegin(); else //the set is empty This will also be constant time instead of linear like the max_element solution.
Yes there is, it is in <algorithm> and is called: std::set_difference. The usage is: #include <algorithm> #include <set> #include <iterator> // … std::set<int> s1, s2; // Fill in s1 and s2 with values std::set<int> result; std::set_difference(s1.begin(), s1.end(), s2.begin(), s2.end(), std::inserter(result, result.end())); In the end, the set result will contain the s1-s2.
I think it was probably because they were trying to make std::set and std::multiset as similar as possible. (And obviously count has a perfectly sensible meaning for std::multiset.) Personally I think this was a mistake. It doesn’t look quite so bad if you pretend that count is just a misspelling of contains and write the … Read more