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

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