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CPP Map

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Maps in CPP are used to store sorted key-value pair. They are the associative containers. Each key in a map is unique. CPP facilitates insertion and deletion of a key in a map but do not allow any modifications, however, values can be modified.

Member Functions of a CPP map:

Allocator:

FUNCTION	USES
get_allocator	To return an allocator object to construct the map.

Capacity:

FUNCTION	USES
empty()	To determine whether the map is empty or not.
max_size()	To determine the maximum size of the map.
size()	To determine number of elements in the map.

Constructor/Destructor:

FUNCTION	USES
(constructor)	To construct a map.
(destructor)	To destruct a map.
operator=	To copy the elements of the map to another map.

Element Access

FUNCTION	USES
at	To get the element with given key.
operator[]	To get the element with given key.

Iterators:

FUNCTION	USES
begin()	To point to the first element of the map.
cbegin()	To return a constant iterator to the beginning of the map.
cend()	To return a constant iterator to the end.
crbegin()	To return a const reverse iterator to the beginning.
crend()	To return a const reverse iterator to the end.
end()	To return an iterator to the end.
rbegin()	To return a reverse iterator to the beginning.
rend()	To return a reverse iterator to the end.

Modifiers:

FUNCTION	USES
clear()	To remove all the elements of the map.
erase()	To delete the specified element.
emplace()	To construct and insert a new element at a specified position.
emplace_hint()	To construct and insert a new element at a specified position by hint.
insert()	To insert a new element in the map..
swap()	To exchange the contents of two maps.

Non-Member Overloaded Functions:

FUNCTION	USES
operator==	To determine whether the two maps are equal or not.
operator!=	To determine whether the two maps are equal or not.
operator<=	To determine whether the first map is less than or equal to other or not.
operator<	To determine whether the first map is less than other or not.
operator>=	To determine whether the first map is greater than equal to other or not.
operator>	To determine whether the first map is greater than other or not.
swap()	To exchange the contents of two maps.

Observers:

FUNCTION	USES
key_comp	To return a copy of key comparison object.
value_comp	To return a copy of value comparison object.

Operations:

FUNCTION	USES
count	To get the number of elements matching with given key.
equal_range	To get the range of elements matches with given key.
find	To find an element with given key.
lower_bound	To get an iterator to lower bound.
upper_bound	To get an iterator to upper bound.

Example:

#include <string.h>  
#include <iostream>  
#include <map>  
#include <utility>  
using namespace std;  
int main()  
{  
map<int, string> Students;  
 
Students[1] = "Vibhu";  
Students[2] = "Yash";  
Students[3] = "Abhi";  
Students[4] = "Neelam";  
cout << "Students[2]=" << Students[2] << "\n\n";  
cout << "Map size: " << Students.size() << endl;  
cout << "\nOrder:" << endl;  
for( map<int,string>::iterator i=Students.begin(); i!=Students.end(); ++i)  
{  
cout << (*i).first << ": " << (*i).second << endl;  
}  
cout << "\nReverse Order:" << endl;  
for( map<int,string>::reverse_iterator i=Students.rbegin(); i!=Students.rend(); ++i)  
{  
cout << (*i).first << ": " << (*i).second << endl;  
}  
}

Output

Students[2]=Yash                     
 
Map size: 4       
 
Order:       
1: Vibhu                          
2: Yash                          
3: Abhi                       
4: Neelam        
 
Reverse Order:                         
4: Neelam                                           
3: Abhi                                  
2: Yash                       
1: Vibhu