C++ | Using std::unordered_map - C++ Full Tutorial

C++ - C++ | Using std::unordered_map

Start

Start
Declaration and Usage As already mentioned you can declare an unordered map of any type. Let's have a unordered map named first with string and integer type. `unordered_map<string, int> first; //declaration of the map first["One"] = 1; // [] operator used to insert the value first["Two"] = 2; first["Three"] = 3; first["Four"] = 4; first["Five"] = 5; pair <string,int> bar = make_pair("Nine", 9); //make a pair of same type first.insert(bar); //can also use insert to feed the values`
Some Basic Functions `unordered_map<data_type, data_type> variable_name; //declaration variable_name[key_value] = mapped_value; //inserting values variable_name.find(key_value); //returns iterator to the key value variable_name.begin(); // iterator to the first element variable_name.end(); // iterator to the last + 1 element` Remarks As the name goes, the elements in unordered map are not stored in sorted sequence. They are stored according to their hash values and hence, usage of unordered map has many benefits such as it only takes O(1) to search any item from it. It is also faster than other map containers. It is also visible from the example that it is very easy to implement as the operator ( [] ) helps us to directly access the mapped value.

Declaration and Usage

As already mentioned you can declare an unordered map of any type. Let's have a unordered map named first with string and integer type.

unordered_map<string, int> first; //declaration of the map 
first["One"] = 1; // [] operator used to insert the value 
first["Two"] = 2;
first["Three"] = 3;
first["Four"] = 4;
first["Five"] = 5;

pair <string,int> bar = make_pair("Nine", 9); //make a pair of same type
first.insert(bar); //can also use insert to feed the values

Some Basic Functions

unordered_map<data_type, data_type> variable_name; //declaration

variable_name[key_value] = mapped_value; //inserting values

variable_name.find(key_value); //returns iterator to the key value

variable_name.begin(); // iterator to the first element

variable_name.end(); // iterator to the last + 1 element

Remarks

As the name goes, the elements in unordered map are not stored in sorted sequence. They are stored according to their hash values and hence, usage of unordered map has many benefits such as it only takes O(1) to search any item from it. It is also faster than other map containers. It is also visible from the example that it is very easy to implement as the operator ( [] ) helps us to directly access the mapped value.

Read Article
https://develop.horje.com/learn/1434/reference