In this article we will see how to use external Sorting Criteria i.e. Comparator in std::set.

Suppose our class is Message that contains three properties i.e.
• Member content
• Sending User Name
• Receiving User Name

we want to keep only single message sent by each user i.e. only one sent message is allowed per user and we can’t modify operator <.


Use external sorting criteria i.e. comparator

Message Class,

Now create a Message comparator,

According to above implementation of comparator two Message objects are compared on the bases of all the sent user name.

So suppose we created 4 Message objects,

Here only msg1, msg2 and msg4 are equal because according to MessageUserComparator implementation.

So, if we insert all the above objects in std::set i.e.

Then out of 4 only 2 will be inserted.

Let’s use the message comparator with std::set of messages,

user_1 :: user_2 :: Hello
user_3 :: user_1 :: Hello

Python Resources

C++11 / C++14 Resources

Design Patterns Resources

If you didn't find what you were looking, then do suggest us in the comments below. We will be more than happy to add that.

Do Subscribe with us for more Articles / Tutorials like this,