Lesson on Maps in C++

Map in C++

Maps are associative containers that store elements in a mapped fashion. Each element has a key value and a mapped value. No two mapped values can have same key values.

To use maps in c++ we need to include map library:

cpp

#include <map>

The map class is generic, meaning you can use it with different types.

Now, let's create a map class object as mymap, that will have key values of data type - string and mapped values of data type - int, these both values are actually stored in pair format, we can also iterate over our map object taking each value in a pair object. To add values in it we can initialize on creation or we can use operator[ ] or the insert() method.

cpp

map<string, int> mymap = {
{"John", 24},
{"Amy", 21}
};
mymap["Hannah"] = 29;
mymap.insert({"Frank", 51});

for(auto [key, value] : mymap)
cout<< key << ":"
<< value << endl;

TRY IT YOURSELF

The map class provides a number of useful functions. Let's take a look at some of the most used ones.

Capacity
empty() checks if the map object is empty.
size() returns the number of keys in the map object.

Modifiers
insert() adds a pair element(one is the key value, and another is map value) in the map object.
erase() removes a key value from the map object.
clear() removes all the keys from the map object.

Element access
operator[ ] returns a reference of the map value for a specified key value in the map object.

The following example demonstrates the use of some of the above mentioned functions:

cpp

cout<< mymap.size()
<< endl;

mymap.clear();

cout<< boolalpha
<< mymap.empty()
<< endl;

mymap["Roxie"] = 35;

mymap.insert({"Russell", 28});

mymap.erase("Russell");

cout<< mymap["Roxie"];

TRY IT YOURSELF

ℹ️ Tap Try it yourself to play around with the code!

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MAP IN C++ | LESSON📖