In C++, the multimap in the Standard Template Library (STL) is an associative container frequently employed to organize key-value pairs in a sorted fashion, enabling the presence of multiple elements with identical keys.
In C++, the function emplace in multimap is frequently used to expand the multimap container by adding new elements directly to the container. The elements are constructed in place, without any copying or moving involved. The element's constructor is invoked with the arguments args provided to this function.
Syntax:
It has the following syntax:
template <class... Args>
iterator emplace (Args&&... args); //since C++ 11
In this structure, the
- args parameter is employed to depict the parameters being passed to construct an element to be added to the multimap.
Return value:
The C++ emplace method signifies whether the insertion has taken place and provides an iterator that points to the recently added element.
C++ Simple multimap emplace function Example
Let's consider a basic scenario to add elements to a multimap using the emplace method in C++.
Example
#include <iostream>
#include <map>
using namespace std;
int main(void) {
multimap<char, int> m;
m.emplace('a', 1);
m.emplace('b', 2);
m.emplace('c', 3);
m.emplace('b', 4);
m.emplace('c', 5);
cout << "Multimap contains the following elements" << endl;
for (auto it = m.begin(); it != m.end(); ++it)
cout << it->first << " = " << it->second << endl;
return 0;
}
Output:
Multimap contains the following elements
a = 1
b = 2
b = 4
c = 3
c = 5
Explanation:
In this illustration, we showcase the application of the multimap::emplace method for directly adding key-value pairs into a multimap without the need for interim objects. This function allows for the insertion of multiple elements with identical keys, ensuring that duplicates are accommodated within the multimap. Through this process, numerous pairs are emplaced within the multimap, resulting in an output that displays all items arranged in ascending order based on keys, with duplicates included.
C++ multimap::emplace Example with Duplicate Keys
Let's consider a basic scenario where we insert an element and verify if a duplicate key is permissible in a multimap data structure in C++.
Example
#include <map>
#include <string>
#include <iostream>
using namespace std; //using standard namespace
template <typename M> void print(const M& m) {
cout << m.size() << " elements: " << endl;
for (const auto& p : m) {
cout << "(" << p.first << "," << p.second << ") ";
}
cout << endl;
}
int main() //main function
{
multimap<string, string> m1;
m1.emplace("Nikita", " Accounting");
m1.emplace("Amita", " Accounting");
m1.emplace("Deep", " Engineering");
cout << "Multimap modified, now contains ";
print(m1);
cout << endl;
m1.emplace("Nikita ", " Engineering");
cout << "Multimap modified, now contains ";
print(m1);
cout << endl;
}
Output:
Multimap modified, now contains 3 elements:
(Amita, Accounting) (Deep, Engineering) (Nikita, Accounting)
Multimap modified, now contains 4 elements:
(Amita, Accounting) (Deep, Engineering) (Nikita, Accounting) (Nikita, Engineering)
Explanation:
In this instance, we are demonstrating the functionality of the multimap::emplace method, which serves to add key-value pairs directly into the container. Given that a multimap supports duplicate keys, it allows for associating multiple values with a single key. For instance, "Nikita" could be linked to both "Accounting" and "Engineering". Subsequently, the items are arranged in ascending order of keys, and the application displays all entries following each insertion.
C++ Example to Show Different Ways to Use the multimap::emplace in C++
Let's consider a basic illustration of adding elements to a multimap in C++ by providing a constructor argument for both a key and a value.
Example
#include <iostream>
#include <utility>
#include <string>
#include <map>
using namespace std; //using standard namespace
int main() //main function
{
multimap<string, string> m;
// uses pair's move constructor
m.emplace(make_pair(string("a"), string("a")));
// uses pair's converting move constructor
m.emplace(make_pair("b", "abcd"));
// uses pair's template constructor
m.emplace("a", "aaa");
// uses pair's piecewise constructor
m.emplace(piecewise_construct,
forward_as_tuple("c"),
forward_as_tuple(10, 'c'));
for (const auto &p : m) {
cout << p.first << " => " << p.second << '\n';
}
}
Output:
a => a
a => aaa
b => abcd
c => cccccccccc
Explanation:
In this instance, we illustrate the multimap::emplace method by adding elements using various constructor variations of std::pair. This showcases adding elements through a standard pair, constructor conversions, direct key-value pairs, and the piecewise_construct method for intricate object generation. Following this, the program displays all added elements, demonstrating the seamless construction of entries through the emplace function.
C++ multimap::emplace Example for Storing Family Member Details
Let's consider an instance to demonstrate how we can save the information of family members utilizing the multimap::emplace method in C++.
Example
#include <iostream>
#include <map>
#include <string>
using namespace std; //using standard namespace
int main() { //main function
typedef multimap<string, int> city;
string name;
int age;
city fmly ;
int n;
cout<<"Enter the number of family members:";
cin>>n;
cout<<"Enter the name and age of each member: \n";
for(int i =0; i<n; i++)
{
cin>> name; // Get key
cin>> age; // Get value
fmly.emplace(name,age); // Put them in multimap
}
cout<<"\nTotal members of the family is: "<< fmly.size();
cout<<"\nDetails of the family members: \n";
cout<<"\nName | Age \n ________________________\n";
city::iterator p;
for(p = fmly.begin(); p!=fmly.end(); p++)
{
cout<<(*p).first << " | " <<(*p).second <<" \n ";
}
return 0;
}
Output:
Enter the number of family members: 3
Enter the name and age of each member:
Jhonson 42
Maddy 37
Michael 40
Total members of the family is: 3
Details of the family members:
Name | Age
__________________________
Jhonson | 40
Maddy | 42
Michael | 37
Explanation:
In this instance, we employ the multimap::emplace method to save information about family members, with names serving as keys and ages as corresponding values. Given that a multimap permits identical keys, it accommodates multiple entries for individuals sharing the same name. Subsequently, the program requests input for each member, adds this data to the multimap, and subsequently displays the total count of members alongside their respective details arranged in alphabetical order based on their names.
Features of Multimap emplace function in C++
There are several features of the multimap emplace function in C++. Some of them are as follows:
- In the C++ programming language, the elements are created in-place inside the container, which helps us to prevent unnecessary operations.
- It takes only (O(log n) time complexity because insertions need to maintain the elements' order.
- It provides exception surety, which means if an exception is thrown, it doesn't affect the container.
- It enables duplicate keys by which the emplace function will insert the elements even if the same key is already present in the multimap.
Conclusion
In summary, the C++ multimap::emplace method offers a practical way to build and add elements directly to a multimap without the need for temporary objects. A multimap allows for the existence of duplicate keys, allowing multiple values to be associated with the same key.
As the emplace function creates elements directly in the container, it offers improved efficiency compared to the insert function in various situations. In general, the emplace function plays a crucial role as a versatile approach for adding elements to a multimap, ensuring sorted arrangement and accommodating duplicate records.
C++ Multimap::emplace function FAQs
The primary purpose of the multimap::emplace function in C++ is to insert a new key-value pair into the multimap container.
In C++, the emplace method is frequently used to construct and add key-value pairs directly into a multimap. This approach avoids the need to create temporary objects, resulting in more efficient insertion when compared to using the insert function.
The time complexity of the multimap::emplace function in C++ is logarithmic, O(log n), where 'n' represents the number of elements in the multimap.
In C++, the time complexity of the multimap::emplace method is O(log n) as it requires preserving the sorted arrangement of elements within the multimap during insertion.
Yes, it is possible to employ the emplace method with an iterator hint in a multimap in C++.
Yes, an overloaded variation is available in the C++ programming language, which allows for the inclusion of a position hint (iterator). This feature can improve the efficiency of insertions when the hint is in proximity to the intended position.
The primary contrast between the emplace and insert functions in C++ lies in how they add elements to a container.
In C++ programming, a key contrast between the emplace and insert functions lies in the fact that emplace is employed to construct elements within the container directly, offering a highly efficient approach. In contrast, insert involves the creation of a temporary object prior to insertion.
5) Is it possible to use the emplace method with intricate objects as a value in C++?
Yes, utilizing the emplace function in C++ allows for the insertion of complex objects as values efficiently, avoiding the need to generate additional temporary copies.
6) The emplace function in C++ ensures that the element orders are preserved in a multimap by inserting new elements based on their keys while maintaining the sorted order of the multimap.
In C++, the multimap data structure is frequently used to store elements in a sorted manner based on keys. The emplace method plays a crucial role in preserving the sorted order when adding new elements.
