Difference between set, multiset, unordered_set, unordered_multiset in C++\\n

Here we will see what are the differences for set, multiset, unordered_set and unordered_multiset in C++. Let us see the properties of them using some example.

Set

The properties of set are like below

• Stores data in sorted order
• Stores only unique values
• We can insert or delete data, but cannot change the data
• We can remove more than one element using start and end iterator
• We can traverse using iterators
• Sets are implemented using Binary Search Tree

Now let us see an example

Example

#include <iostream> #include <set> using namespace std; main() {    int data[15] = {11, 55, 22, 66, 33, 22, 11, 44, 77, 88, 66, 99, 66, 23, 41};    set<int> my_set;    for(int i = 0; i<15; i++) {       my_set.insert(data[i]);    }    set<int>::iterator it;    for(it = my_set.begin(); it != my_set.end(); it++) {       cout << "Item: " << *it << endl;    } }

Output

Item: 11 Item: 22 Item: 23 Item: 33 Item: 41 Item: 44 Item: 55 Item: 66 Item: 77 Item: 88 Item: 99

Multiset

The properties of set are like below −

• Stores data in sorted order
• It allows to store duplicate data
• We can remove more than one element using start and end iterator.

Now let us see an example.

Example

#include <iostream> #include <set> using namespace std; main() {    int data[15] = {11, 55, 22, 66, 33, 22, 11, 44, 77, 88, 66, 99, 66, 23, 41};    multiset<int> my_set;    for(int i = 0; i<15; i++) {       my_set.insert(data[i]);    }    multiset<int>::iterator it;    for(it = my_set.begin(); it != my_set.end(); it++) {       cout << "Item: " << *it << endl;    } }

Output

Item: 11 Item: 11 Item: 22 Item: 22 Item: 23 Item: 33 Item: 41 Item: 44 Item: 55 Item: 66 Item: 66 Item: 66 Item: 77 Item: 88 Item: 99

Unordered Set

The properties of set are like below −

• Data can be placed in any order
• Duplicate data will be discarded
• This set is created using Hash-tables
• We can erase only one element, where the iterator is pointing

Now let us see an example.

Example

#include <iostream> #include <unordered_set> using namespace std; main() {    int data[15] = {11, 55, 22, 66, 33, 22, 11, 44, 77, 88, 66, 99, 66, 23, 41};    unordered_set<int> my_set;    for(int i = 0; i<15; i++) {       my_set.insert(data[i]);    }    unordered_set<int>::iterator it;    for(it = my_set.begin(); it != my_set.end(); it++) {       cout << "Item: " << *it << endl;    } }

Output

Item: 11 Item: 55 Item: 22 Item: 66 Item: 33 Item: 44 Item: 77 Item: 88 Item: 99 Item: 23 Item: 41

Unordered Multiset

The properties of set are like below −

• Data can be placed in any order
• Duplicate data are allowed
• This set is created using Hash-tables
• We can erase only one element, where the iterator is pointing

Now let us see an example.

Example

#include <iostream> #include <unordered_set> using namespace std; main() {    int data[15] = {11, 55, 22, 66, 33, 22, 11, 44, 77, 88, 66, 99, 66, 23, 41};    unordered_multiset<int> my_set;    for(int i = 0; i<15; i++) {       my_set.insert(data[i]);    }    unordered_multiset<int>::iterator it;    for(it = my_set.begin(); it != my_set.end(); it++) {       cout << "Item: " << *it << endl;    } }

Output

Item: 11 Item: 55 Item: 22 Item: 66 Item: 33 Item: 22 Item: 11 Item: 44 Item: 77 Item: 88 Item: 66 Item: 99 Item: 66 Item: 23 Item: 41