C++ multiset emplace
The emplace function in C++ for multiset is employed to enlarge the multiset container by adding fresh elements directly into the container without copying or moving them.
The element's constructor is invoked by providing the arguments passed to this function.
Syntax
template <class? Args>
iterator emplace (Args&&? args); //since C++ 11
Parameter
The parameters passed to create an element for insertion into the container.
Return value
The emplace method provides a boolean pair to signal whether the insertion took place and yields an iterator pointing to the newly added element.
Complexity
Logarithmic in the container size.
Iterator validity
No changes.
Data Races
The container is modified.
Iterating over ranges within the container poses a safety risk, whereas simultaneous access to existing elements remains secure.
Exception Safety
If an error is raised, the multiset container remains unchanged.
Example 1
Let's explore a straightforward example of adding elements to the multiset:
#include <iostream>
#include <set>
using namespace std;
int main(void) {
multiset<char> m;
m.emplace('a');
m.emplace('b');
m.emplace('a');
m.emplace('c');
m.emplace('b');
cout << "Multiset contains following elements" << endl;
for (auto it = m.begin(); it != m.end(); ++it)
cout << *it<< ", ";
return 0;
}
Output:
Multiset contains following elements
a, a, b, b, c,
In the aforementioned example, it merely adds the element to the multiset m using the provided values.
Example 2
Let's examine a basic example to insert the element and validate the presence of a duplicate key:
#include <set>
#include <string>
#include <iostream>
using namespace std;
template <typename S> void print(const S& s) {
cout << s.size() << " elements: ";
for (const auto& p : s) {
cout << "(" << p << ") ";
}
cout << endl;
}
int main()
{
multiset<string> s1;
s1.emplace("Deep");
s1.emplace("Nikita");
s1.emplace("Kesharwani");
cout << "multiset modified, now contains ";
print(s1);
cout << endl;
s1.emplace("Nikita");
cout << "multiset modified, now contains ";
print(s1);
cout << endl;
}
Output:
multiset modified, now contains 3 elements: (Deep) (Kesharwani) (Nikita)
multiset modified, now contains 4 elements: (Deep) (Kesharwani) (Nikita) (Nikita)
Example 3
Let's explore a basic example to calculate the total of the provided values:
#include <iostream>
#include <set>
using namespace std;
int main()
{
// sum variable declaration
int sum = 0;
// multiset declaration
multiset<int> mymultiset{};
mymultiset.emplace(1);
mymultiset.emplace(3);
mymultiset.emplace(4);
mymultiset.emplace(1);
mymultiset.emplace(2);
mymultiset.emplace(2);
mymultiset.emplace(3);
// iterator declaration
multiset<int>::iterator it;
// finding sum of elements
while (!mymultiset.empty()) {
it = mymultiset.begin();
sum = sum + *it;
mymultiset.erase(it);
}
// printing the sum
cout << "Sum of elements is: "<<sum;
return 0;
}
Output:
Sum of elements is: 16
Example 4
Let's see a simple example to insert the element:
#include <iostream>
#include <set>
#include <string>
using namespace std;
int main() {
typedef multiset<string> city;
string name;
city fmly ;
int n;
cout<<"Enter the number of family members :";
cin>>n;
cout<<"Enter the name of each member: \n";
for(int i =0; i<n; i++)
{
cin>> name; // Get key
fmly.emplace(name);
}
cout<<"\nTotal member of family is:"<< fmly.size();
cout<<"\nDetails of family members: \n";
cout<<"\nName \n ________________________\n";
city::iterator p;
for(p = fmly.begin(); p!=fmly.end(); p++)
{
cout<<(*p)<<" \n ";
}
return 0;
}
Output:
Enter the number of family members: 3
Enter the name of each member:
Bob
Robin
David
Total member of family is: 3
Details of family members:
Name
________________________
Bob
David
Robin
In the example provided, it merely inserts the elements based on the user's selection.
