C++ Map Library - begin() Function

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Description

The C++ function std::map::begin() returns a iterator which refers to the first element of the map.

Declaration

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

C++98

iterator begin();
const_iterator begin() const;

C++11

iterator begin() noexcept;
const_iterator begin() const noexcept;

Parameters

None

Return value

If object is constant qualified then method returns constant iterator otherwise it returns non-constant reference.

Exceptions

This member function never throws exception.

Time complexity

Constant i.e. O(1)

Example

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

#include <iostream>
#include <map>

using namespace std;

int main(void) {
   /* Initializer_list constructor */
   map<char, int> m = {
            {'a', 1},
            {'b', 2},
            {'c', 3},
            {'d', 4},
            {'e', 5},
            };

   cout << "Map contains following elements" << endl;

   for (auto it = m.begin(); it != m.end(); ++it)
      cout << it->first << " = " << it->second << endl;

   return 0;
}

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

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