Use of multisets in C duplicate

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I understand the use of sets in C++, but why are there multisets?

What are some examples of real-world uses for multisets?

This argument may be extended to unordered multisets as well; what distinguishes it from utilising a vector, and what benefits and drawbacks does it provide?
Jun 27 in C++ by Nicholas
• 5,020 points
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1 answer to this question.

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Because a multi-set does not need the storage of single-element objects. 

You're considering storing anything in a multi-set, such as a string. 

But it is not its intended use. 

You may use whatever struct you want and compare it to a single element in the struct.

As an example:

struct PhoneBookEntry
{
    std::string name;
    std::string phoneNumber;
}

There's no reason to have a single entry per name in a phone book in this unsophisticated "phone book" entry. 

There may be a lot. 

So you create a PhoneBookEntry multiset and make the comparator by name. 

You may have many phone numbers with the same name this way.

You could assume that a map is more appropriate for this. 

However, this is only one example. 

A multiset is used when you don't require a key/value pair but need the search features of a set with several entries per key.

answered Jun 27 by Damon
• 4,960 points

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