map::at() and map::swap() in C++ STL
Maps are the container in STL which is used to store the elements in the form of key-value pair. Internally, the elements in a map are always sorted by its key. Maps are mainly implemented as binary search trees.
map::at()
at() function is used to return the reference to the element associated with the key k.
Syntax:
map1.at(k) Parameters: k is the Key value of the element whose associated value is accessed.
Return: It return a reference to the associated value of the element whose key value is equivalent to k.
Examples:
Input: map1 = {
{1, 'a'},
{2, 'b'},
{3, 'c'},
{4, 'd'}
}
map1.at(2);
Output: b
Input: map2 = {
{'w', 1},
{'x', 2},
{'y', 3}
}
map2.at('w');
Output: 1
// CPP program to illustrate// Implementation of swap() function#include <bits/stdc++.h>using namespace std; int main(){ // Take any two maps map<int, char> map1; map<char, int> map2; map1[1] = 'a'; map1[2] = 'b'; map1[3] = 'c'; map1[4] = 'd'; map2['w'] = 1; map2['y'] = 2; map2['z'] = 3; // Print the associated element cout << "Element at map1[2] = " << map1.at(2) << endl; cout << "Element at map2['w'] = " << map2.at('w') << endl; return 0;} |
Output:
Element at map1[2] = b Element at map2['w'] = 1
map::swap()
swap() function is used to exchange the contents of two maps but the maps must be of same type, although sizes may differ.
Syntax:
map1.swap(map2)
OR
swap(map1, map2)
Parameters:
map1 is the first map object.
map2 is the second map object.
Return value: None
Examples:
Input : map1 = {
{1, 'a'},
{2, 'b'},
{3, 'c'},
{4, 'd'}
}
map2 = {
{5, 'w'},
{6, 'x'},
{7, 'y'}
}
swap(map1, map2)
Output : map1 = {
{5, 'w'},
{6, 'x'},
{7, 'y'}
}
map2 = {
{1, 'a'},
{2, 'b'},
{3, 'c'},
{4, 'd'}
}
// CPP program to illustrate// Implementation of swap() function#include <bits/stdc++.h>using namespace std; int main(){ // Take any two maps map<int, char> map1, map2; map1[1] = 'a'; map1[2] = 'b'; map1[3] = 'c'; map1[4] = 'd'; map2[5] = 'w'; map2[6] = 'x'; map2[7] = 'y'; // Swap elements of queues swap(map1, map2); // Print the elements of maps cout << "map1:\n" << "\tKEY\tELEMENT\n"; for (auto it = map1.begin(); it != map1.end(); it++) cout << "\t" << it->first << "\t" << it->second << '\n'; cout << "map2:\n" << "\tKEY\tELEMENT\n"; for (auto it = map2.begin(); it != map2.end(); it++) cout << "\t" << it->first << "\t" << it->second << '\n'; return 0;} |
Output:
map1:
KEY ELEMENT
5 w
6 x
7 y
map2:
KEY ELEMENT
1 a
2 b
3 c
4 d
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