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C++ Program to Implement Map in STL
A Map is an associative container 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.
Functions are used here:
m::find() – Returns an iterator to the element with key value ‘b’ in the map if found, else returns the iterator to end.
m::erase() – Removes the key value from the map.
m:: equal_range() – Returns an iterator of pairs. The pair refers to the bounds of a range that includes all the elements in the container which have a key equivalent to key.
m insert() – To insert elements in the map container.
m size() – Returns the number of elements in the map container.
m count() – Returns the number of matches to element with key value ‘a’ or ‘f’ in the map.
Example Code
#include<iostream>
#include <map>
#include <string>
using namespace std;
int main () {
map<char, int> m;
map<char, int>::iterator it;
m.insert (pair<char, int>('a', 10));
m.insert (pair<char, int>('b', 20));
m.insert (pair<char, int>('c', 30));
m.insert (pair<char, int>('d', 40));
cout<<"Size of the map: "<< m.size() <<endl;
cout << "map contains:\n";
for (it = m.begin(); it != m.end(); ++it)
cout << (*it).first << " => " << (*it).second << '\n';
for (char c = 'a'; c <= 'd'; c++) {
cout << "There are " << m.count(c) << " element(s) with key " << c << ":";
map<char, int>::iterator it;
for (it = m.equal_range(c).first; it != m.equal_range(c).second; ++it)
cout << ' ' << (*it).second;
cout << endl;
}
if (m.count('a'))
cout << "The key a is present\n";
else
cout << "The key a is not present\n";
if (m.count('f'))
cout << "The key f is present\n";
else
cout << "The key f is not present\n";
it = m.find('b');
m.erase (it);
cout<<"Size of the map: "<<m.size()<<endl;
cout << "map contains:\n";
for (it = m.begin(); it != m.end(); ++it)
cout << (*it).first << " => " << (*it).second << '\n';
return 0;
}Output
Size of the map: 4 map contains: a => 10 b => 20 c => 30 d => 40 There are 1 element(s) with key a: 10 There are 1 element(s) with key b: 20 There are 1 element(s) with key c: 30 There are 1 element(s) with key d: 40 The key a is present The key f is not present Size of the map: 3 map contains: a => 10 c => 30 d => 40
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