std::unordered_set Basic Usage & Example
std::unordered_set is an STL container and its introduced in C++11. It provides a functionality of a Set i.e. it can contains the unique elements only. unordered_set stores the elements internally using a Hash Table.
We can declare an unordered_set of a particular type only i.e.
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std::unordered_set<T> setOfTypeT; |
Elements of Type with which an unoredered_set is declared can only be added in it. Also, all elements of Type T should be,
- Copyable or Movable
- Comparable
Above requirements are because of the reason that element added in unordered_set will act as both key and value for internal Hash Table. As it’s a key therefore it should be comparable and copy-able.
Also, all elements in the unordered_set are immutable i.e. they can not be modified once inserted. They can only be deleted after the insertion.
Header File Required is,
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#include <unordered_set> |
Creating and using an std::unordered_set of std::string
As all objects of type std::string is copy-able and comparable. So, let’s create an unordered_set of type std::string and use it i.e.
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std::unordered_set<std::string> setOfStrs; |
Here, as we have declared an unordered set of type std::string. It means it can only store unique strings. Let’s see a complete example,
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#include <iostream> #include <unordered_set> #include <algorithm> int main() { // Creating an Unoredered_set of type string std::unordered_set<std::string> setOfStrs; // Insert strings to the set setOfStrs.insert("First"); setOfStrs.insert("second"); setOfStrs.insert("third"); // Try to Insert a duplicate string in set setOfStrs.insert("second"); // Iterate Over the Unordered Set and display it for (std::string s : setOfStrs) std::cout << s << std::endl; } |
Output:
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third second First |
Here we added 4 elements in the unoredered_set but only 3 will get added, last insertion will not work because “second” is already inserted in set and unoredered_set contains only the unique elements.
Thanks.
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