Iterators are one of the most useful features of containers in modern C++. Mostly we use them with vectors, maps, strings, and other containers of C++. In C++11, the begin() and end() iterators are used to define the start of iteration and the end of the iteration, mostly used in the for loops. In C++14, there are new additions to the global std::begin – std::end functions, and in this post, we explain these new begin-end iterators.
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What are the begin end iterators in C++11 and beyond?
In modern C++, containers are data storage arrays. They are very useful for iterating and searching data with their amazing methods and properties. An iterator (<iterator>) is an object that points to an element in a range of elements (i.e. characters of a string or members of a vector). We can use Iterators to iterate through the elements of this range using a set of operators, for example using the ++, –, and * operators.
Iteration can be done with begin/end iterators,
- The
begin()method returns an iterator pointing to the first element in the vector. - The
end()method returns an iterator pointing to the theoretical element that follows the last element in the vector.
Here is a simple example how we can use begin end iterators in the for iteration as below.
What are the reverse begin end iterators in C++14?
In C++14 , there are new additions to the global std::begin – std::end functions, they were augmented with reverse iterators, std::rbegin and std::rend. These are available in C++17 too.
Reverse iteration can be done with rbegin and rend iterators.
- The
rbegin()method returns a reverse iterator pointing to the last element in the vector. It moves from last to first element. - The
rend()method returns a reverse iterator pointing to the theoretical element preceding the first element in the vector.
Here is an example with a vector vec.
this list vector members in reverse order.
What are the constant begin end iterators in C++14?
In C++14 and C++17, there are also constant begin end iterators. std::cbegin and std::cend , and reverse iterators std::rbegin/std::rend and std::crbegin and std::crend
Constant iteration can be done with with cbegin/cend iterators, this can be faster than normal iteration.
- The
cbegin()method returns a constant iterator pointing to the first element in the vector. - The
cend()method returns a constant iterator pointing to the theoretical element that follows the last element in the vector.
Here is an example with a vector vec.
this list vector members in constant iterators.
What are the constant reverse begin end iterators in C++14?
In C++14 and C++17, constant reverse iterations can be done with crbegin and crend iterators,
- The crbegin() method returns a constant reverse iterator pointing to the last element in the vector. It moves from last to first element.
- The crend() method returns a constant reverse iterator pointing to the theoretical element preceding the first element in the vector.
Here is an example with a vector vec.
this list vector members as a constant iterator in reverse order.
Is there a full example about new begin end iterators in C++14?
Here is a full example about how we can use new begin end iterators in C++ and beyond.
and the output will be as follows:
Note that these can be applied to the other containers of the modern C++, such as strings, arrays, lists, maps, sets, etc.
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