# C++ set equal_range()

C++ set equal_range() function is used to return the boundary of the range containing all elements in the container that are equal to val. Since there is no duplication of values in the set container, this range includes at most one element.

If val does not match any value in the container, the return value range will be length 0 and both iterators will point to the nearest value greater than val. Otherwise, if val is greater than all elements in the container, it points to end.

## Syntax

The range is defined by two iterators, one points to the first element that is not less than value val and another points to the first element greater than value val.

## Parameter

val: value to be searched in the set container.

## Return value

This function returns pair. Where pair:: first is at the lower boundary of the range with the same value that lower_bound (val) would return, pair :: second is the same value as the upper_bound (val) would return, upper bound of the range it corresponds to.

## Complexity

Logarithmic in size.

No changes.

## Data Races

The container is accessed (neither the const not non-const versions modify the container).

Concurrently accessing the elements of a set is safe.

## Exception Safety

If an exception is thrown, there are no changes in the container.

## Example 1

Let's see the simple example:

Output:

```Lower bound of b is: b
Upper bound of b is: c
```

In the above example, lower bound of b is b and upper bound of b is c.

## Example 2

Let's see a simple example:

Output:

```The lower bound is 3
The upper bound is 3
```

In the above example, equal_range() function returns to the end() i.e. 3 because it tries to find 10 which is not present in the set mp.

## Example 3

Let's see a simple example:

Output:

```The upper bound of the element with a key of 20 in the set s1 is: 30.
The lower bound of the element with a key of 20 in the set s1 is: 20.
A direct call of upper_bound( 20 ) gives 30,
matching the 2nd element of the pair returned by equal_range( 20 ).
The set s1 doesn't have an element with a key less than 40.
```

## Example 4

Let's see a simple example:

Output:

```The lower bound points to: 30
The upper bound points to: 40
```

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