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Sets

Introduction to Sets in Standard Template Library​

Sets are a type of associative container in the Standard Template Library (STL) of C++. They are mainly used to store unique elements following a specific order. In a set, the value of the element also identifies it (the value is itself the key, of type T), and each value must be unique.

How to Declare a Set​

To declare a set, you can use the following syntax:

std::set<datatype> setname;

Here, datatype could be any valid C++ data type and setname is the name of the set.

For example:

std::set<int> mySet;

The above line declares a set of integers with the name mySet.

Basic Operations​

Sets in C++ STL provide several functions to perform different operations. Some of the basic ones include:

  • insert(): This function is used to insert elements into the set. 
mySet.insert(30); // inserts 30 into the set
  • erase(): This function is used to remove elements from the set. It can erase elements by their value or by their position.
mySet.erase(30); // erases 30 from the set
  • find(): This function returns an iterator to the element if it is found, otherwise it returns an iterator to set::end.
auto it = mySet.find(20); // finds 20 in the set
  • size(): This function returns the number of elements present in the set.
int size = mySet.size(); // returns the size of the set
  • empty(): This function returns true if the set is empty, otherwise false.
bool isEmpty = mySet.empty(); // checks if the set is empty

Set Iterators​

Just like other STL containers, sets too have iterators. You can declare an iterator for a set as follows:

std::set<int>::iterator it;

You can iterate through the elements of a set using the iterator:

for (it = mySet.begin(); it != mySet.end(); it++)
{
    std::cout << *it << " ";
}

Set Characteristics​

Here are some key points to remember about sets:

  • Sets are typically implemented as binary search trees.
  • Insertion, removal, and search operations have logarithmic complexity.
  • Sets do not allow for modification of its elements. This is because the modification could potentially violate the set's ordering property.
  • If you need to change a value in a set, the correct approach is to remove the old value and insert the new one.

Conclusion​

Sets in C++ STL are powerful tools that allow us to deal with a group of unique elements in a sorted manner. They provide a variety of built-in functions which makes it easy to implement and manipulate sets. However, keep in mind that the elements of a set are always sorted and unique, which makes it different from other containers such as vectors or lists.