C++ Map Library - empty() Function

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Description

The C++ function std::map::empty() tests whether map is empty or not. Map of size zero is considered as empty map.

Declaration

Following is the declaration for std::map::empty() function form std::map header.

C++98

bool empty() const noexcept;

C++11

bool empty() const;

Parameters

None

Return value

Returns true if map is empty otherwise false.

Exceptions

This member function never throws exception.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::map::empty() function.

#include <iostream>
#include <map>

using namespace std;

int main(void) {
   /* Initializer_list constructor */
   map<char, int> m;

   if (m.empty())
      cout << "Map is empty" << endl;

   m.emplace('a', 1);

   if (!m.empty())
      cout << "Map is not empty" << endl;

   return 0;
}

Let us compile and run the above program, this will produce the following result −

Map is empty
Map is not empty