C++ Forward_list Library - before_begin() Function

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Description

The C++ function std::forward_list::before_begin() returns a random access iterator which points to the position before the first element of the forward_list.

This iterator can be used with emplace_after, erase_after, insert_after and splice_after.

Declaration

Following is the declaration for std::forward_list::before_begin() function form std::forward_list header.

C++11

iterator before_begin() noexcept;
const_iterator before_begin() const noexcept;

Parameters

None

Return value

If forward_list object is constant qualified then method returns constant random access iterator otherwise non constant random access iterator.

Exceptions

This member function never throws exception.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::forward_list::before_begin() function.

#include <iostream>
#include <forward_list>

using namespace std;

int main(void) {

   forward_list<int> fl = {2, 3, 4, 5};
   auto it = fl.before_begin();

   fl.insert_after(it, 1);

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

   for (auto it = fl.begin(); it != fl.end(); ++it)
      cout << *it << endl;

   return 0;
}

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

List contains following elements
1
2
3
4
5