C++ Map Library - map() Function

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Description

The C++ constructor std::map::map() constructs an empty map with zero elements.

Declaration

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

C++98

explicit map (const key_compare& comp = key_compare(),
              const allocator_type& alloc = allocator_type());

C++11

explicit map (const key_compare& comp = key_compare(),
              const allocator_type& alloc = allocator_type());
explicit map (const allocator_type& alloc);

Parameters

• comp − A binary predicate, which takes two key arguments and returns true if first argument goes before second otherwise false. By default it uses less<key_type> predicate.

• alloc − The allocator object.

Return value

Constructor never returns value.

Exceptions

This member function never throws exception.

Time complexity

Constant i.e. O(1)

Example

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

#include <iostream>
#include <map>

using namespace std;

int main(void) {
   map<char, int> m;

   cout << "Size of map = " << m.size() << endl;

   return 0;
}

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

Size of map = 0