Get the best out of our app
GeeksforGeeks App
Open App
Browser
Continue

# multiset::emplace() in C++ STL

Multisets are a type of associative containers similar to set, with an exception that multiple elements can have same values.

multiset::emplace()

This function is used to insert a new element into the multiset container.

Syntax :

```multisetname.emplace(value)
Parameters :
The element to be inserted into the multiset
is passed as the parameter.
Result :
The parameter is added to the multiset.
```

Examples:

```Input  : mymultiset{1, 2, 3, 4, 5};
mymultiset.emplace(6);
Output : mymultiset = 1, 2, 3, 4, 5, 6

Input  : mymultiset{};
mymultiset.emplace("This");
mymultiset.emplace("is");
mymultiset.emplace("Geeksforgeeks");
Output : mymultiset = Geeksforgeeks, This, is
```

Errors and Exceptions
1. It has a strong exception guarantee, therefore, no changes are made if an exception is thrown
2. Parameter should be of same type as that of the container, otherwise an error is thrown

 `// INTEGER EXAMPLE``// CPP program to illustrate``// Implementation of emplace() function``#include ``#include ``using` `namespace` `std;`` ` `int` `main()``{``    ``multiset<``int``> mymultiset{};``    ``mymultiset.emplace(1);``    ``mymultiset.emplace(56);``    ``mymultiset.emplace(4);``    ``mymultiset.emplace(9);``    ``mymultiset.emplace(0);``    ``// multi set becomes 0, 1, 4, 9, 56`` ` `    ``// adding another element``    ``mymultiset.emplace(87);`` ` `    ``// printing the multiset``    ``for` `(``auto` `it = mymultiset.begin();``         ``it != mymultiset.end(); ++it)``        ``cout << ``' '` `<< *it;``    ``return` `0;``}`

Output:

```0 1 4 9 56 87
```

 `// STRING EXAMPLE``// CPP program to illustrate``// Implementation of emplace() function``#include ``#include ``#include ``using` `namespace` `std;`` ` `int` `main()``{``    ``multiset mymultiset{};``    ``mymultiset.emplace(``"This"``);``    ``mymultiset.emplace(``"is"``);``    ``mymultiset.emplace(``"a"``);``    ``mymultiset.emplace(``"computer science"``);``    ``mymultiset.emplace(``"portal"``);``    ``// multi set becomes This, a,``    ``// computer science, is, portal`` ` `    ``// adding element``    ``mymultiset.emplace(``"GeeksForGeeks"``);`` ` `    ``// printing the multiset``    ``for` `(``auto` `it = mymultiset.begin();``         ``it != mymultiset.end(); ++it)``        ``cout << ``' '` `<< *it;``    ``return` `0;``}`

Output:

```GeeksForGeeks This a computer science is portal
```

Application
Input an empty multi set with the following numbers and order using emplace() function and find sum of elements. The advantage of emplace() over insert is, it avoids unnecessary copy of object.

```Input :  7, 9, 4, 6, 2, 5, 3
Output : 36```

 `// CPP program to illustrate``// Application of emplace() function``#include ``#include ``using` `namespace` `std;`` ` `int` `main()``{``    ``// sum variable declaration``    ``int` `sum = 0;`` ` `    ``// multiset declaration``    ``multiset<``int``> mymultiset{};``    ``mymultiset.emplace(7);``    ``mymultiset.emplace(9);``    ``mymultiset.emplace(4);``    ``mymultiset.emplace(6);``    ``mymultiset.emplace(2);``    ``mymultiset.emplace(5);``    ``mymultiset.emplace(3);`` ` `    ``// iterator declaration``    ``set<``int``>::iterator it;`` ` `    ``// finding sum of elements``    ``while` `(!mymultiset.empty()) {``        ``it = mymultiset.begin();``        ``sum = sum + *it;``        ``mymultiset.erase(it);``    ``}`` ` `    ``// printing the sum``    ``cout << sum;``    ``return` `0;``}`

Output :

```36
```

Time Complexity : O(logn)

emplace() vs insert()
When we use insert, we create an object and then insert it into the multiset. With emplace(), the object is constructed in-place.

 `// C++ code to demonstrate difference between``// emplace and insert``#include``using` `namespace` `std;`` ` `int` `main()``{``    ``// declaring multiset of pairs``    ``multiset> ms;``     ` `    ``// using emplace() to insert pair in-place``    ``ms.emplace(``'a'``, 24);``     ` `    ``// Below line would not compile``    ``// ms.insert('b', 25);    ``     ` `    ``// using insert() to insert pair in-place``    ``ms.insert(make_pair(``'b'``, 25));    ``     ` `    ``// printing the multiset``    ``for` `(``auto` `it = ms.begin(); it != ms.end(); ++it)``        ``cout << ``" "` `<< (*it).first << ``" "` `             ``<< (*it).second << endl;`` ` `    ``return` `0;``}`

Output :

``` a 24
b 25
```

Please refer Inserting elements in std::map (insert, emplace and operator []) for details.

My Personal Notes arrow_drop_up