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C++ - INSERT IN MAP

How to insert a new Entry in a Map?

Let us say, we have a Map that contains,

Five, Is a Number

John, Is a Name

C++, Is a Language

As Key and Value pair.

Now, let us say, we want to insert a new entry,

Rose, Is a Flower

Where Rose is the Key and Is a Flower is its corresponding Value.

Let us see in the below example.

Example :

#include <iostream>
#include <map>

using namespace std;

int main() {

    map<string, string> x = 
        {
	        { "Five", "Is a Number" }, 
	        { "John", "Is a Name" }, 
	        { "C++", "Is a Language"}
        };
        
    x["Rose"] = "Is a Flower";
        
    for (auto i : x)  
    {  
        cout << "The Key is : " << i.first << " and the Value is :"  << i.second << endl;  
    }
    
    return 0;    
}

Output :

The key is : Five and the value is : Is a Number
The key is : John and the value is : Is a Name
The key is : C++ and the value is : Is a Language
The key is : Rose and the value is : Is a Flower

So, in the above code we have created a Map using braces {} and Key and Value pairs.

map<string, string> x =
	{
		{ "Five", "Is a Number" },
		{ "John", "Is a Name" },
		{ "C++", "Is a Language"}
	};

And initialised to the variable x.

Now, we are supposed to add a new entry to the Map. Where the Key would be Rose and the Value Is a Flower.

So, we have used the below way to add it.

x["Rose"] = "Is a Flower";

And the entry is added to the Map.

And we get the below output,

Output :

The key is : Five and the value is : Is a Number
The key is : John and the value is : Is a Name
The key is : C++ and the value is : Is a Language
The key is : Rose and the value is : Is a Flower

The insert() method is also used to insert a new Entry into a Map.

Insert a new Entry in a Map using insert() method

Let us rewrite the above example,

Example :

#include <iostream>
#include <map>

using namespace std;

int main() {

    map<string, string> x = 
        {
	        { "Five", "Is a Number" }, 
	        { "John", "Is a Name" }, 
	        { "C++", "Is a Language"}
        };
        
    x.insert({"Rose", "Is a Flower"});
        
    for (auto i : x)  
    {  
        cout << "The Key is : " << i.first << " and the Value is :"  << i.second << endl;  
    }
    
    return 0;    
}

Output :

The key is : Five and the value is : Is a Number
The key is : John and the value is : Is a Name
The key is : C++ and the value is : Is a Language
The key is : Rose and the value is : Is a Flower

So, in the above code we have created a Map using braces {} and Key and Value pairs.

map<string, string> x =
	{
		{ "Five", "Is a Number" },
		{ "John", "Is a Name" },
		{ "C++", "Is a Language"}
	};

And initialised to the variable x.

Now, we are supposed to add a new entry to the Map. Where the Key would be Rose and the Value Is a Flower.

So, we have used the insert() method to add it.

x.insert({"Rose", "Is a Flower"});

And the entry is added to the Map.

And we get the below output,

Output :

The key is : Five and the value is : Is a Number
The key is : John and the value is : Is a Name
The key is : C++ and the value is : Is a Language
The key is : Rose and the value is : Is a Flower

Duplicate Keys are not allowed in Map

Let us say, we have a Map that contains,

Five, Is a Number

John, Is a Name

C++, Is a Language

As Key and Value pair.

Now, let us say, we want to insert a new entry,

John, Is an English Name

Where John is the Key and Is an English Name is its corresponding Value.

Let us see in the below example.

Example :

#include <iostream>
#include <map>

using namespace std;

int main() {

    map<string, string> x = 
        {
	        { "Five", "Is a Number" }, 
	        { "John", "Is a Name" }, 
	        { "C++", "Is a Language"}
        };
        
    x["John"] = "Is an English Name";
        
    for (auto i : x)  
    {  
        cout << "The Key is : " << i.first << " and the Value is :"  << i.second << endl;  
    }
    
    return 0;    
}

Output :

The Key is : C++ and the Value is :Is a Language
The Key is : Five and the Value is :Is a Number
The Key is : John and the Value is :Is an English Name

So, for the Key, John the initial value was Is a Name.

map<string, string> x =
	{
		{ "Five", "Is a Number" },
		{ "John", "Is a Name" },
		{ "C++", "Is a Language"}
	};

And we wanted to add a new entry with the Key as John and the Value as Is an English Name.

x["John"] = "Is an English Name";

But if we see the output.

Output :

The Key is : C++ and the Value is :Is a Language
The Key is : Five and the Value is :Is a Number
The Key is : John and the Value is :Is an English Name

We can see the Key, John is updated with the Value, Is an English Name.

That's because duplicate Keys are not allowed in Map. The corresponding value for that Key will get updated with the new Value.

Note : Just remember, only duplicate 'Keys' are not allowed in a 'Map'. However, you can have duplicate 'Values'.

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