forward_list::cbefore_begin() in C++ STL

To faithfully explain the concept of forward_list::cbefore_begin() in C++ STL. We first discussed the List in C++n programming language's code and output below. The forward list c before begin function is an in-built functionality in STL [Standard Template Library (STL)]. It returns a constant random-access iterator which points to the position before the first element of the forward_list.

List in C++ STL

C++ code

// CPP program to show the implementation of List
// Here we are writing down the C++ programming language code to 
// demonstrate the concept of List in C++ programming language code
// in the Standard Template Library (STL)
#include <iostream>
#include <iterator>
#include <list>
using namespace std;

// function for printing the elements in a list
// the below few lines of code help us with displaying the elements that
// we have inserted into it which is a part of the C++ Standard Template 
// Library (STL)
void showlist(list<int> g)
{
	list<int>::iterator it;
	for (it = g.begin(); it != g.end(); ++it)
		cout << '\t' << *it;
	cout << '\n';
}

// the main driver code functionality starts from here
int main()
{

// then below code helps us with creating a list in C++ STL dynamically
	list<int> gqlist1, gqlist2;
// loop to push elements into the list which we have just created
	for (int i = 0; i < 10; ++i) {
		gqlist1.push_back(i * 2);
		gqlist2.push_front(i * 3);
	}
	// cout statement helping us to print gqlist1 elements on console
	cout << "\nThe List 1 has elements  : ";
	showlist(gqlist1);
    // cout statement helping us to print gqlist2 elements on console
	cout << "\nThe List 2 has elements : ";
	showlist(gqlist2);
    // cout statement helping us to print gqlist1 front elements on console
	cout << "\n list1.front() : " << gqlist1.front();
	// cout statement helping us to print gqlist1 back elements on console
	cout << "\n list1.back() : " << gqlist1.back();
//cout statement helping us to print gqlist after poping elements on console
	cout << "\n list1.pop_front() : ";
	gqlist1.pop_front();
	showlist(gqlist1);
//cout statement helping us to print list after poping elements on console
	cout << "\n list2.pop_back() : ";
	gqlist2.pop_back();
	showlist(gqlist2);
//cout statement helping us to print gqlist after reverse elements on 
// console
	cout << "\n list1.reverse() : ";
	gqlist1.reverse();
	showlist(gqlist1);
//cout statement helping us to print gqlist after sort elements on console
	cout << "\n list2.sort(): ";
	gqlist2.sort();
	showlist(gqlist2);

	return 0;
	// end of the C++ programming language code explaining 
	// forward_list::cbefore_begin() in C++ STL

}

Output:

The List 1 has elements  : 	0	2	4	6	8	10	12	14	16	18

List 2 has elements : 	27	24	21	18	15	12	9	6	3	0

 list1.front() : 0
 list1.back() : 18
 list1.pop_front() : 	2	4	6	8	10	12	14	16	18

 list2.pop_back() : 	27	24	21	18	15	12	9	6	3

 list1.reverse() : 	18	16	14	12	10	8	6	4	2

list2.sort(): 	3	6	9	12	15	18	21	24	27

Syntax of forward_list::cbefore_begin()

C++ code

// Here we are writing down the c++ programming language code to 
// demonstrate the concept of forward_list::cbefore_begin() in C++ STL
// where it illustrates the function cbefore_begin() in C++ programming code
#include <bits/stdc++.h>
using namespace std;
// the main driver code functionality starts from here
int main()
{
	// the below code snippet helps us with creating a list with few
	// initial values like 20, 30, 40 and ends with 50
	forward_list<int> fl = { 20, 30, 40, 50 };

	// here, we are trying to perform the function
	// cbefore_begin helping us to use the stl library in the C++ language
	auto it = fl.cbefore_begin();

	// the below code snippet helps us with the insertion operation 
	// where the element will be added to the first place
	fl.insert_after(it, 10);

	cout << "the elements which have gotten inserted are as follows" << endl;

	// the below for loop helps us with printing down the
	// elements, which we have created in the list on our output screens
	for (auto it = fl.begin(); it != fl.end(); ++it)
		cout << *it << " ";

	return 0;
	// end of the C++ programming language code explaining 
	// forward_list::cbefore_begin() in C++ STL
}

Output:

the elements which have gotten inserted are as follows
10 20 30 40 50

Next TopicHeap in C++ STL | make_heap(), push_heap(),pop_heap(), sort_heap(), is_heap, is_heap_until()

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