Sets

Sets are associative containers which store unique elements that can be referenced by an element’s value. The value, which is itself the key to access an element in the set, is constant. Once assigned it cannot be changed. However, existing values can be removed or new values can be added.

Syntax

std::set<dataType> setName;

A set can be created by using the set keyword and declaring a data type and name.

Example

The example below initiates a set, inserts values into it using the .insert() method, and then prints out the set:

#include <iostream>
#include <set>
int main(){
// Initiate set
std::set<int> numSet;
// Insert values into set
numSet.insert(25);
numSet.insert(42);
numSet.insert(10);
numSet.insert(19);
// Print out set
std::set<int> :: iterator iter;
for(iter = numSet.begin(); iter != numSet.end(); iter++)
{
std::cout<< *iter << " ";
}
}

This outputs the following:

10 19 25 42

By default, values of the set are sorted in ascending order.

Setting a Different Comparison Function

The comparison function can be changed from the default to std::greater<dataType> in order to sort the values in descending order.

Syntax

std::set<dataType, std::greater<dataType> > setName;

The dataType for the comparison function must match the data type of the set.

Codebyte Example

Setting the previous example’s comparison function to std::greater<int>:

Code
Output
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Sets

.clear()
Removes all values from a set.
.erase()
Removes a single value from a set.
.insert()
Inserts a single value into a set.

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