The C++ programming language has a lot of options to add and modify data members with their amazing data holders, arrays, structs, pointers and containers. Containers are powerful data storage arrays in C++ and they are very useful to iterate and search. A container is a holder object that stores data elements (a collection of data objects). std::vector, std::array, std::set, std::list are these kinds of containers. There is another useful container std::forward_list, in this post, we explain what std::forward_list is. Before that let’s remind ourselves what containers are in C++ programming and what are their types.
Table of Contents
What is a container in modern C++?
Containers are modern data storage arrays in modern C++ and they are very useful to iterate and search data with their amazing methods and properties.
A container is a holder object that stores data elements (a collection of data objects). They are implemented as a class template to define objects that can be used with modern rules of C++ (The rule of 6), they allow great flexibility in the different data types supported as elements, they can be used with int, float, double, etc. or with struct types, they can be used with other modern types of C++, lambdas and templates. Thus, the developer can create different data sets in memory, these can be static or dynamic, they are safe and optimized well.
What are the basic container types modern C++?
The C++ Standards library defines 4 container types.
- Sequence Containers ( vector, array, deque, list, forward_list )
- Associative Containers ( map, multimap, set, multiset )
- Unordered Associative Containers ( unordered_map, unordered_multimap, unordered_set, unordered_multiset )
- Container Adapters ( stack, queue, priority_queue )
If you want to learn more about these each type, here are some basic details,
What is std::forward_list in modern C++?
The forward_list (std::forward_list) is a sequence container class template defined in <forward_list> header that supports forward iterations, and faster insert and delete operations. The std::forward_list does not invalidate pointers or references of its members when you use these insertion methods or deletion methods as in std::list and std::deque, while the std::vector does. They support only forward iterations and do not support bidirectional iterations, and because of this, they use less memory space than the std::list. If you do not need backward iterations in a list, then it is much better to use std::forward_list
In general, std::forward_list is defined as below.
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template < class T, class Allocator = std::allocator< T > > class forward_list; |
Since C++17, std::forward_list is improved and defined in the pmr namespace as below.
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namespace pmr { template< class T > using forward_list = std::forward_list< T, std::pmr::polymorphic_allocator< T > >; } |
Is there a simple std::forward_list example in modern C++?
Here is a simple std::forward_list declaration example in C++.
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std::forward_list<int> lst; |
we can define its member in definition as below.
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std::forward_list<int> lst = { 50, 100 }; |
Or we can use push_front methods to add new members on runtime.
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std::forward_list<int> lst; lst.push_front(100); lst.push_front(50); |
and there is no push_back method because of being forward list.
What is std::forward_list in modern C++?
Here is a full example about std::forward_list
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#include <iostream> #include <forward_list> int main() { std::forward_list<int> lst; // Forward list in integers lst.push_front(50); lst.push_front(100); lst.push_front(200); lst.push_front(300); for(auto L : lst) { std::cout << L << " , "; } std::cout << std::endl; system("pause"); return 0; } |
and the output will be as follows,
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300 , 200 , 100 , 50 , |
For more new details, please check these papers, p0646r1 and n2543
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