unordered_map empty in C++ STL (original) (raw)

Last Updated : 12 Jun, 2023

unordered_map::empty() function is used to check whether container size is zero or not. If container size is zero then it return TRUE otherwise it return FALSE.

Syntax:

unordered_map_name.empty()

Parameters: This function does not accept any parameter

Return type: This function returns boolean value TRUE or FALSE.

Examples:

Input: ump = { {1, 2}, {3, 4}, {5, 6}, {7, 8}} ump.empty();
Output: False

Input: ump = { }; ump.empty();
Output: True

CPP `

// CPP program to illustrate // Implementation of unordered_map empty() function #include <bits/stdc++.h> using namespace std;

int main() { // Take any two unordered_map unordered_map<int, int> ump1, ump2;

// Inserting values
ump1[1] = 2;
ump1[3] = 4;
ump1[5] = 6;
ump1[7] = 8;

// Print the size of container
cout << "ump1 size = " << ump1.size() << endl;
cout << "ump2 size = " << ump2.size() << endl;

// Running the function for ump1
if (ump1.empty())
    cout << "True\n";
else
    cout << "False\n";

// Running the function for ump2
if (ump2.empty())
    cout << "True\n";
else
    cout << "False\n";

// Running the function for ump1 after
// clearing it
ump1.clear();
if (ump1.empty())
    cout << "True\n";
else
    cout << "False\n";

return 0;

}

`

Output:

ump1 size = 4 ump2 size = 0 False True True

Time complexity: O(1).

Auxiliary space: O(n). // n is the total number of elements in the unordered_map.