C++ multimap equal_range()

C++ multimap equal_range() function is used to return the boundary of the range containing all key elements in the container which is equal to x.

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

Syntax

The range is defined by two iterators. It returns the bounds of a range that includes all the elements in the container which have a key equivalent to k.

Parameter

k: key to be searched in the multimap 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 (x) would return, pair :: second is the same value as the upper_bound (x) would return, upper bound of the range it corresponds to.

Complexity

Logarithmic in size.

Iterator validity

No changes.

Data Races

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

No mapped values are accessed: concurrently accessing and modifying the elements 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 = 2
Upper bound of b is: c = 3

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 3:0
The upper bound is 3:0

In the above example, equal_range() function returns 0 because it tries to find 10 which is not the key of the multimap mp.

Example 3

Let's see a simple example:

Output:

The lower bound of the element with a key of 2 in the multimap m1 is: 20.
The upper bound of the element with a key of 2 in the multimap m1 is: 30.
A direct call of upper_bound( 2 ) gives 30,
 matching the 2nd element of the pair returned by equal_range( 2 ).
The multimap m1 doesn't have an element with a key less than 4.

Example 4

Let's see a simple example:

Output:

B, 1