C++ Forward_list Library - cbefore_begin() Function

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Description

The C++ function std::forward_list::cbefore_begin() returns a constant 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.

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::forward_list::cbefore_begin() function form std::forward_list header.

C++11

const_iterator cbefore_begin() const noexcept;

Parameters

None

Return value

Returns a 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::cbefore_begin() function.

#include <iostream>
#include <forward_list>

using namespace std;

int main(void) {

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