C++ Unordered_map Library - cbegin() Function

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Description

The C++ function std::unordered_map::cbegin() returns a constant iterator which refers to the first element of the unordered_map.

Iterator obtained by this member function can be used to iterate container but cannot be used to modify the content of object to which it is pointing even if object itself is not constant.

Declaration

Following is the declaration for std::unordered_map::cbegin() function form std::unordered_map header.

C++11

const_iterator cbegin() const noexcept;

Parameters

None

Return value

Returns constant iterator.

Exceptions

This member function never throws exception.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::unordered_map::cbegin() function.

#include <iostream>
#include <unordered_map>

using namespace std;

int main(void) {
   unordered_map<char, int> um = {
            {'a', 1},
            {'b', 2},
            {'c', 3},
            {'d', 4},
            {'e', 5}
            };

   cout << "Unordered map contains following elements" << endl;

   for (auto it = um.cbegin(); it != um.cend(); ++it)
      cout << it->first << " = " << it->second << endl;

   return 0;
}

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

Unordered map contains following elements
e = 5
a = 1
b = 2
c = 3
d = 4