C++ .swap()

In C++, .swap() function exchanges the contents of two maps in constant time, provided the maps are of the same type, though their sizes may differ.

Syntax

map1.swap(map2);

• map1: The first map whose contents will be swapped.
• map2: The second map to exchange contents with map1.

Note: If map1 and map2 are not of the same type (i.e., they do not have the same key and value types), a compilation error will occur because std::map::swap() requires both maps to have the same type.

Example

The following example shows how the swap() funcrion works:

#include <iostream>
#include <map>
using namespace std;

int main() {
    map<int, string> map1{{1, "one"}, {2, "two"}, {3, "three"}};
    map<int, string> map2{{4, "four"}, {5, "five"}, {6, "six"}};

    cout << "Before swap Map1:\n";
    for(map<int, string>::iterator it = map1.begin();it != map1.end();++it) {
        cout << "Key: " << it->first<< ", Value: " << it->second << endl;
    }

    cout << "Before swap Map2:\n";
    for(map<int, string>::iterator it = map2.begin();it != map2.end();++it) {
        cout << "Key: " << it->first<< ", Value: " << it->second << endl;
    }

    // Swapping the contents of map1 and map2
    map1.swap(map2);

    cout << "After swap Map1:\n";
    for(map<int, string>::iterator it = map1.begin();it != map1.end();++it) {
        cout << "Key: " << it->first<< ", Value: " << it->second << endl;
    }

    cout << "After swap Map2:\n";
    for(map<int, string>::iterator it = map2.begin();it != map2.end();++it) {
        cout << "Key: " << it->first<< ", Value: " << it->second << endl;
    }

    return 0;
}

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The output of the above code will be:

Before swap Map1:
Key: 1, Value: one
Key: 2, Value: two
Key: 3, Value: three
Before swap Map2:
Key: 4, Value: four
Key: 5, Value: five
Key: 6, Value: six
After swap Map1:
Key: 4, Value: four
Key: 5, Value: five
Key: 6, Value: six
After swap Map2:
Key: 1, Value: one
Key: 2, Value: two
Key: 3, Value: three

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Codebyte Example

Run the below codebyte example to know how the .swap() function works:

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