Dimensional Data

The C++17 standard came with a lot of great features and std::optional was one of the main features of today’s modern C++. std::optional is a class template that is defined in the header and represents either a T value or no value. In this post, we explain, what is optional in modern C++ and how we can use it efficiently. What is the optional class template in C++ 17 and beyond? The std::optional feature is a class template that is defined in the header and represents either a T value or no value (which is signified by the tag type nullopt_t). In some respects, this can be thought of as equivalent to variant, but with a purpose-built interface. Here is the definition of the std::optional class template.   template class optional;   Optional can be used to define any type of variables as below.   std::optional a(5); std::optional b;   An optional variable can be checked by has_value() method if it has a value or not.   if (a.has_value()) { }   Here is another example that has a function with an optional return.   std::optional testopt(std::string s) { if(s.length()==0) return {}; else return s; }   as you see our function may return a string as an option or it may have no return value. A common use case for optional is the return value of a function that may fail. Any instance of optional at any given point in time either contains a value or does not contain a value. If an optionalcontains a value, the value is guaranteed to be allocated as part of the optional object footprint, i.e. no dynamic memory allocation ever takes place. Thus, an optional object models an object, not a pointer, even though operator*() and operator->() are defined. Is there a simple example about the optional class template in C++ 17? Here is a simple example about the std::optional, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19   #include #include   int main() { std::optional a(5);  // a = 5 std::optional b;   // b has no value   if (a.has_value())         { int z = a.value() + b.value_or(0); std::cout

C++17 had enormous changes in C++ features. One of them was basic_string_view (std::basic_string_view) which is a constant string container that can be used for multiple string declarations. The basic_string_view is a modern way of read-only text definition. It can be used by iterators and other methods of the basic_string_view class. In this post, we explain basic_string_view and its types. What is basic_string_view in modern C++ In the Library Fundamentals Technical Specification (LFTS), The C++ commitee introduced std::basic_string_view, and it was approved for C++17. The basic_string_view (std::basic_string_view) is a class template defined in the header that is used to define a constant string container that can be used to define multiple strings which refers to the contiguous character sequence, and the first element of this sequence position at the zero position. The basic_string_view is a modern way of read-only text definition, it can be used by iterators, and other methods of the basic_string_view class can be used.  Here is the syntax of the basic_string_view:   template class basic_string_view;   We can use different character types in std::basic_string_view types as same as std::basic_string. The std::basic_string_view has 5 different string types, these are, std::string_view, std::wstring_view, std::u8string_view, std::u16string_view, and std::u32string_view. The std::string_view provides read-only access to a string definition with chars as similar to the interface of std::string. In addition to this, we can use std::wstring_view, std::u16string_view, and std::u32string_view in C++17. There is std::u8string_view that is added by the C++20 standards too. Here are the basic_string_types and their features. Type Char Type Definition Standard std::string_view char std::basic_string_view (C++17) std::wstring_view wchar_t std::basic_string_view (C++17) std::u8string_view char8_t std::basic_string_view (C++20) std::u16string_view char16_t std::basic_string_view (C++17) std::u32string_view char32_t std::basic_string_view (C++17) Is there an example about basic_string_view in modern C++ Here is a C++ example that we use std::string_view, std::wsting_view, std::u16string_view, std::u32string_view in C++17. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30   #include #include #include   int main() { const std::string_view  sview = “This is a stringview example”; const std::wstring_view wsview = L“This is a stringview example”; const std::u16string_view u16sview = u“This is a stringview example”; const std::u32string_view u32sview = U“This is a stringview example”;   const std::string_view sviews[]{ “This is “, “LearnCPlusPlus.org “, “and welcome “, “!” };   for ( auto sv : sviews) { std::cout

One of the great features of C++ is templates, they are parameterized by alias templates in C++11. Then, In C++14 and C++17, they improved C++11’s feature with a number of template aliases whose use simplifies the traits. This feature is called “Alias Templates For Traits” and in this post, we explain what is and alias template and how we can use alias templates with traits. What is a template In C++ ? A template is a simple and a very powerful statement in C++ which defines the operations of a class or function and lets the user apply the same template on different types in those operations. A template defines the operations of a class, a function, it is an alias. For example, we can create an add(a,b) function template as shown below.   template T add (T a, T b) {   return a+b; }   What is a type alias, and an alias template in C++ 11? Type Alias is a term that refers to a previously defined types, alias declaration can be used to declare a name to use as a synonym for a previously declared type. We use using declaration (using-declaration) to declare a type alias, and it is effectively the same as typedef. This can be in block scope, class scope, or namespace scope. Type alias does not introduce a new type and it cannot change the usage or meaning of an existing type name. A type alias declaration is completely the same as typedef declaration. Type alias can be used to create an alias template that can be used as a custom allocator. Type alias which comes after C++11 standard, is used to create an alias template which can be used as a custom allocator. An alias template is an alias that uses a template which refers to a family of types. For example, let’s create a table template which has type, rows and cols parameters. We can create this table (my_table) template as below,   // A Template Example template class my_table { };   We can use this template to create two more alias templates. Here we create a single column (my_column) and a single row (my_row) templates as below,   // Alias Template Example template using my_column = my_table; template using my_row = my_table;   As you see, we have a my_table template and my_column, my_row templates which are alias templates of the my_table template. These templates can be used to with any data types (int, float, char, string, wstring, etc.). Now we can use all the templates to create a table which has rows and columns or a single row or a single column data in a given type. Here is how we can use them,      my_table  table1;    my_column col1;    my_row row1;   What are the alias templates for traits in C++ 14? In C++17, there are alias templates for type traits, they are defined in header and they can be used by using #include . In C++17, they improved C++11’s TransformationTraits feature with a number of template aliases whose use simplifies the traits. According to N3655 paper, “A TransformationTrait modifies a property of a type. It shall be a class template that takes one template-type argument and, optionally, additional arguments that help define the modification. It shall define a nested type1 named type, which shall be a synonym for the modified type.” In […]

C++17 standard is amazing with a lot of new features, and one of the interesting features was the new type std::any. std::any is a type-safe container to store a single value of any variable type. In this post, we explain std::any in modern C++. What is std::any in C++ 17 ? The any class (std::any) is a new class defined in the  header in C++17 and it is used for any type definition, it is a safe type container for single values that are copy constructible. The std::any is a container type that is used to store any value in it without worrying about the type safety of the variable. It has been designed based on boost::any from the boost library. It is very useful, when you have a variable, and you want to change its type (int to float) on runtime. Here is the simplified syntax for std::any.   std::any ;   Here is a simple definition example. The std::any is a type-safe container that has properties such as has_value(), type(), type().name(); it has modifiers such as emplace, reset, swap; it has bad_any_cast helper class, and it can be used with other methods such as make_any, any_cast, std::swap. How can we use std::any in C++ 17? Here is a simple example how we can use the std::any with different types in C++17 and beyond.   #include   int main() { std::any a;     a = true; // boolean a = 100;  // integer a = 9.81; // double }   In some definitions, we can use literals to define type of the variable, let’s see example below. Is there a full example about how can we use std::any in C++ 17? Here is a full example about std::any that shows different any definitions. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42   #include #include #include #include #include   using namespace std::literals;   int main() { std::any a; std::cout