Dictionary in C++

A dictionary can be implemented in C++ with the help of std::map of standard template library (STL). It can implement sorted key-value pairs with unique keys. We can alter, search, remove and insert the values associated with the keys in a map within O(N) time complexity. But we can only insert or delete the keys, we cannot alter them.
In this article, we will discuss different ways to create a dictionary in C++ and basic functions which are associated with it.
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How to create a dictionary in C++?

We can initialize a dictionary using different methods. Let’s understand them:

In C++, the key-value pairs are separated by commas and curly brackets are used for initialization. Methods to create a dictionary are given below:

Code:

#include 
#include 
#include 
using namespace std;

int main() {

    //METHOD 1: Using Initializer List
    map language = {{1, "Java",},
                                {2, "Python",},
                                {3, "C++",},
                                {4, "Javascript"},
                                };

    map::iterator itr;

    //Printing the map: language
    cout << "The map language is : \n";
    cout << "\tKEY\tELEMENT\n";
    for (itr = language.begin(); itr != language.end(); ++itr) {
        cout << '\t' << itr->first
            << '\t' << itr->second << '\n';
    }
    cout << endl;

    //METHOD 2: Using default constructor
    map fruits;
        fruits[1] = "Banana";
        fruits[2] = "Mango";
        fruits[3] = "Cocoa";
        fruits[4] = "Raspberry";

    //Printing the map: fruits
    cout << "The map fruits is : \n";
    cout << "\tKEY\tELEMENT\n";
    for (itr = fruits.begin(); itr != fruits.end(); ++itr) {
        cout << '\t' << itr->first
            << '\t' << itr->second << '\n';
    }
    cout << endl;

    //METHOD 3: Using Insert() function and Pair
    map cars;
    cars.insert(pair(1, "Honda"));
    cars.insert(pair(2, "Toyota"));
    cars.insert(pair(3, "Maruti"));
    cars.insert(pair(4, "Mercedes"));

    //Printing the map: cars
    cout << "The map cars is : \n";
    cout << "\tKEY\tELEMENT\n";
    for (itr = cars.begin(); itr != cars.end(); ++itr) {
        cout << '\t' << itr->first
            << '\t' << itr->second << '\n';
    }
    cout << endl;

    //Method 4: New dictionary with copied values from different dictionary
    //Creating map2 with language map values

    map map2(language);

    //Printing the map: map2
    cout << "The map map2 is : \n";
    cout << "\tKEY\tELEMENT\n";
    for (itr = map2.begin(); itr != map2.end(); ++itr) {
        cout << '\t' << itr->first
            << '\t' << itr->second << '\n';
    }
    cout << endl;

    //Method 5: Creating new dictionary by copying key-value pairs in a specific range
    map map3(fruits.find(3), fruits.end());

    //Printing the map: map3
    cout << "The map map3 is : \n";
    cout << "\tKEY\tELEMENT\n";
    for (itr = map3.begin(); itr != map3.end(); ++itr) {
        cout << '\t' << itr->first
            << '\t' << itr->second << '\n';
    }
    cout << endl;

    return 0;
}

Output:

The map language is :
KEY ELEMENT
1 Java
2 Python
3 C++
4 Javascript

The map fruits is :
KEY ELEMENT
1 Banana
2 Mango
3 Cocoa
4 Raspberry

The map cars is :
KEY ELEMENT
1 Honda
2 Toyota
3 Maruti
4 Mercedes

The map map2 is :
KEY ELEMENT
1 Java
2 Python
3 C++
4 Javascript

The map map3 is :
KEY ELEMENT
3 Cocoa
4 Raspberry

Member functions associated with Map in C++:

Modifiers

clear(): It can be used to empty the map.
erase(): It will remove the element which is stored at the iterator position, or value at the given key, or in the range as well.
pair insert(key, value): It is used to add new elements in the map.
swap(map): Exchanges the elements of two containers.
emplace(): It will insert a new key-value pair in the map if there is no equivalent key present in the map before the execution of this function.

Code:

#include 
#include 
#include 
using namespace std;

template
void print(Map &m)
{
   cout << "[ ";
    for (auto &item : m) {
        cout << item.first << ":" << item.second << " ";
    }
    cout << "]\n";
}

int main() {

    map::iterator it1;
    map::iterator it2;
    map dictionary = {{1, "Java",},
                                {2, "Python",},
                                {3, "C++",},
                                {4, "Javascript",},
                                {5, "PHP",},
                                {6, "C#",},
                                {7, "Pascal",},
                                {8, "Spring",}};
   //ERASE FUNCTION
    it1=dictionary.begin();   
    dictionary.erase(it1);   //erasing by iterator

    dictionary.erase(2);    //erasing by key

    it1=dictionary.find(3);          
    it2=dictionary.find(5);
    dictionary.erase(it1,it2); //erasing by range
    cout<<"Map after erase:";
    print(dictionary);

    //INSERT FUNCTION
    dictionary.insert(pair(1, "Java"));
    dictionary.insert(pair(2, "Python"));
    dictionary.insert(pair(3, "C++"));
    dictionary.insert(pair(4, "Javascript"));
    dictionary.insert(pair(9, "SQL"));
    cout<<"\nMap after insert:";
    print(dictionary);

    //SWAP FUNCTION
    map map2;
    map2[1]="Honda";
    map2[2]="Mercedes";
    map2[3]="Audi";
    map2[4]="Toyota";
    dictionary.swap(map2);
    cout<<"\nMap2 conains:";
    print(map2);
    cout<<"\nDictionary contains:";
    print(dictionary);

    //EMPLACE FUNCTION
    dictionary.emplace(5,"Porsche");
    dictionary.emplace(6, "Rolls Royce");
    cout<<"\nAfter emplace:";
    print(dictionary);
  //CLEAR FUNCTION
    dictionary.clear();
    cout<<"\nAfter Clear:";
    print(dictionary);

    return 0;
}

Output:

Map after erase:[ 5:PHP 6:C# 7:Pascal 8:Spring ]

Map after insert:[ 1:Java 2:Python 3:C++ 4:Javascript 5:PHP 6:C# 7:Pascal 8:Spring 9:SQL ]

Map2 conains:[ 1:Java 2:Python 3:C++ 4:Javascript 5:PHP 6:C# 7:Pascal 8:Spring 9:SQL ]

Dictionary contains:[ 1:Honda 2:Mercedes 3:Audi 4:Toyota ]

After emplace:[ 1:Honda 2:Mercedes 3:Audi 4:Toyota 5:Porsche 6:Rolls Royce ]

After Clear:[ ]

Capacity

empty(): It will check if the map is empty
size(): It will return the number of key-value pairs in the map.
max_size(): It will return the maximum number of elements that the map can hold. Example: It can be used to check beforehand whether the map will allow for 1000 elements to be inserted.

Code:

#include 
#include 
using namespace std;

template
void print(Map &m)
{
   cout << "[ ";
    for (auto &item : m) {
        cout << item.first << ":" << item.second << " ";
    }
    cout << "]\n";
}

int main(){
    map dictionary = {{1, "Java",},
                                {2, "Python",},
                                {3, "C++",},
                                {4, "Javascript",},
                                };

    //Size fucntion                          
    cout<<"Size of dictionary(map) is:"<< dictionary.size();

    //max_size function
    cout<<"\nDictionary can hold: "<< dictionary.max_size()<<" values";
    if (dictionary.max_size()>1000){
        cout<<"\nThis map can hold more than 1000 values.";
    }
    else{
        cout<<"This map cannot hold 1000 values.";
    }

    //empty function
    if(dictionary.empty())
    {
    cout<<"\nDictionary is empty";
    }
    else
    {
        cout<<"\nDictionary is not empty";
    }

    return 0;
}

Output:

Size of dictionary(map) is:4
Dictionary can hold: 384307168202282325 values
This map can hold more than 1000 values.
Dictionary is not empty

Iterators

begin(): Returns an iterator to the first element in the map.
end(): Returns an iterator to the last element in the map.
rbegin() It will return a reverse iterator which will be pointing to the last element in the container. Reverse iterator iterates backwards.
rend(): It will return a reverse iterator which will point to the first element in the container.

Code:

#include 
#include 
#include 
using namespace std;

int main() {

    map::iterator it;
    map dictionary = {{1, "Java",},
                                {2, "Python",},
                                {3, "C++",},
                                {4, "Javascript",},
                               };

    //PRINTING dictionary USING BEGIN() & END() FUNCTION
    cout<<"USING BEGIN & END";
    cout << "\nElements in dictionary are : \n";
    cout << "\tKEY\tELEMENT\n";
    for(it=dictionary.begin();it!=dictionary.end(); it++)
    {
        cout << '\t' << it->first
            << '\t' << it->second << '\n';
    }

    //PRINTING USING RBEGIN() & REND()

    map::reverse_iterator itr;
    cout<<"USING RBEGIN & REND";
    cout << "\nElements in dictionary are : \n";
    cout << "\tKEY\tELEMENT\n";
    for(itr=dictionary.rbegin();itr!=dictionary.rend(); ++itr)
    {
        cout << '\t' << itr->first
            << '\t' << itr->second << '\n';
    }

    return 0;
}

Output:

USING BEGIN & END
Elements in dictionary are :
KEY ELEMENT
1 Java
2 Python
3 C++
4 Javascript
USING RBEGIN & REND
Elements in dictionary are :
KEY ELEMENT
4 Javascript
3 C++
2 Python
1 Java

Operations

find(k): It will search for the key x in the container and will return an iterator if found or it will take the iterator to the end.
count(x): It will search for the key x in the container and will return the number of matches.
lower_bound(): It returns an iterator pointing to the first element whose key is not considered to go before ‘x’(it will be either equivalent or greater)
upper _bound():It returns an iterator pointing to the element whose key is considered to go after ‘x’. It returns an iterator pointing to the next element where it finds the equivalent key.
equal_range(): It returns a pair of iterators. Pair means the bounds of a range which will include all the elements in the container which have a key equivalent to ‘x’. Maps only have unique keys, so the first iterator in the pair points to the next key that is after ‘x’.

Code:

#include 
#include 
#include 
using namespace std;

int main() {

    map::iterator it1,it2,it3;
    map dictionary = {{1, "Java",},
                                {2, "Python",},
                                {3, "C++",},
                                {4, "Javascript",},
                              };
    //USING FIND FUNCTION
    cout<<"Element 1 Value="<second;
    cout<<"\nElement 2 Value="<second<<"\n";

    //USING COUNT FUNCTION
    //Find out if the elements are present in the map or not
    for(int i=1; i<7;i++)
    {
        cout<0)
        {
            cout<<"is an element of dictionary.\n";
        }
        else
        {
            cout<<"is not an element of dictionary.\n";
        }
    }

    //USING LOWER BOUND AND UPPER BOUND
    it1=dictionary.lower_bound(2);  //points to key:2
    it2=dictionary.upper_bound(4);  //points to 5 (not 4)

    dictionary.erase(it1,it2);  //erases elements from it1 to it2
        //printing the dictionary
    for(it3=dictionary.begin();it3!=dictionary.end(); it3++)
    {
        cout<first <<"=" <second <<'\n';
    }

    //USING EQUAL_RANGE
        map dictionary2 = {{1, "Java",},
                                {2, "Python",},
                                {3, "C++",},
                                {4, "Javascript",},
                               };
    pair::iterator,map::iterator> it4;
    it4=dictionary2.equal_range(2);

    //printing
    cout<<"\nLower bound points to= ";
    cout<first <<" --> " <second ;

    cout<<"\nUpper bound points to= ";
    cout<first<<" --> "<second;

    return 0;
}

Output:

Element 1 Value=Java
Element 2 Value=Python
1 is an element of dictionary.
2 is an element of dictionary.
3 is an element of dictionary.
4 is an element of dictionary.
5 is not an element of dictionary.
6 is not an element of dictionary.
1=Java

Lower bound points to= 2 --> Python
Upper bound points to= 3 --> C++

Conclusion

In this article, we discussed methods to create a dictionary in C++ and its member functions which can be used to perform different types of operations.

That's all about Dictionary in C++.
Happy Learning!!

How to create a dictionary in C++?

Modifiers

Capacity

Iterators

Operations

Conclusion

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How to create a dictionary in C++?

Modifiers

Capacity

Iterators

Operations

Conclusion

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