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Use a reverse_iterator to go from the end to the beginning
/* Use a reverse_iterator to go from the end to the beginning */
#include <iostream>
#include <list>
#include <algorithm>
#include <string>
using namespace std;
static const int ARRAY_SIZE = 5;
int main( ) {
list<string> lstStr;
lstStr.push_back("A");
lstStr.push_back("B");
lstStr.push_back("C");
lstStr.push_back("D");
for (list<string>::iterator p = lstStr.begin( );
p != lstStr.end( ); ++p) {
cout << *p << endl;
}
for (list<string>::reverse_iterator p = lstStr.rbegin( );
p != lstStr.rend( ); ++p) {
cout << *p << endl;
}
}
/*
A
B
C
D
D
C
B
A
*/
Iterators are just like pointers used to access the container elements. Iterators are one of the four pillars of the Standard Template Library or STL in C++. An iterator is used to point to the memory address of the STL container classes. For better understanding, you can relate them with a pointer, to some extent. Iterators act as a bridge that connects algorithms to STL containers and allows the modifications of the data present inside the container. They allow you to iterate over the container, access and assign the values, and run different operators over them, to get the desired result. • Iterators are used to traverse from one element to another element, a process is known as iterating through the container. • The main advantage of an iterator is to provide a common interface for all the containers type. • Iterators make the algorithm independent of the type of the container used.
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Add element at the end. Adds a new element at the end of the list container, after its current last element. The content of val is copied (or moved) to the new element. This effectively increases the container size by one. The list:push_back() function in C++ STL is used to add a new element to an existing list container. It takes the element to be added as a parameter and adds it to the list container. This function accepts a single parameter which is mandatory value. This refers to the element needed to be added to the list, list_name. This function does not return any value.
Return reverse iterator to reverse end. Returns a reverse iterator pointing to the theoretical element preceding the first element in the list container (which is considered its reverse end). The C++ list::rend function returns the reverse iterator pointing to the element preceding the first element (reversed past-the-last element) of the list. A reverse iterator iterates in backward direction and increasing it results into moving to the beginning of the list container. Similarly, decreasing a reverse iterator results into moving to the end of the list container. The range between list::rbegin and list::rend contains all the elements of the container (in reverse order).
This class reverses the direction in which a bidirectional or random-access iterator iterates through a range. A copy of the original iterator (the base iterator) is kept internally and used to reflect the operations performed on the reverse_iterator: whenever the reverse_iterator is incremented, its base iterator is decreased, and vice versa. A copy of the base iterator with the current state can be obtained at any time by calling member base. Notice however that when an iterator is reversed, the reversed version does not point to the same element in the range, but to the one preceding it. This is so, in order to arrange for the past-the-end element of a range: An iterator pointing to a past-the-end element in a range, when reversed, is pointing to the last element (not past it) of the range (this would be the first element of the reversed range). And if an iterator to the first element in a range is reversed, the reversed iterator points to the element before the first element
Return iterator to end. Returns an iterator referring to the past-the-end element in the list container. The past-the-end element is the theoretical element that would follow the last element in the list container. It does not point to any element, and thus shall not be dereferenced. Because the ranges used by functions of the standard library do not include the element pointed by their closing iterator, this function is often used in combination with list::begin to specify a range including all the elements in the container. If the container is empty, this function returns the same as list::begin. This function does not accept any parameter.
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Return iterator to beginning. Returns an iterator pointing to the first element in the list container. Notice that, unlike member list::front, which returns a reference to the first element, this function returns a bidirectional iterator pointing to it. If the container is empty, the returned iterator value shall not be dereferenced. begin() function is used to return an iterator pointing to the first element of the list container. It is different from the front() function because the front function returns a reference to the first element of the container but begin() function returns a bidirectional iterator to the first element of the container. This function does not accept any parameter. Function returns an iterator to the beginning of the sequence container.
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#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
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Return reverse iterator to reverse beginning. Returns a reverse iterator pointing to the last element in the container (i.e., its reverse beginning). list::rbegin() is an inbuilt function in C++ STL which is declared in header file. rbegin() is a reverse begin function. rebegin() returns a reverse iterator which is pointing to the last element of the list. Reverse iterator is an iterator which moves in reverse direction, starting from the end and will move towards the start. However back() also returns the last element but unlike the simple iterator this bidirectional iterator moves in backward direction. Reverse iterators iterate backwards: increasing them moves them towards the beginning of the container. rbegin points to the element right before the one that would be pointed to by member end.
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