Dimensional Data

The auto keyword arrives with the new features of the C++11 and the standards above. In C++14, there is a new decltype that is used with auto keyword. In modern C++, the decltype(auto) type-specifier deduces return types while keeping their references and cv-qualifiers, while auto does not. In this post, we explain what decltype (auto) is in modern C++ and how to use it. What is auto in modern C++? The auto keyword is used to define variable types automatically, it is a placeholder type specifier (an auto-typed variable), or it can be used in a function declaration, or a structured binding declaration. If you want to learn more about auto keyword, here it is, What is decltype in modern C++? The decltype keyword and operator represents the type of a given entity or expression. This feature is one of the C++11 features added to compilers (including BCC32 and other CLANG compilers). In a way you are saying “I am declaring this variable to be the same type as this other variable“. Here are more details about how you can use it, How to use decltype (auto) in modern C++? In C++14, there is a new decltype feature that allows you to use with the auto keyword. In C++14 and standards above, the decltype(auto) type-specifier deduces return types while keeping their references and cv-qualifiers, while auto does not. Since C++14, here is the syntax,   type_constraint (optional) decltype ( auto )   In this syntax, the type is decltype(expr) and expr can be an initializer or a return statement. Here is a simple example how we can use it,   decltype(auto) x = i;   Are there some simple examples about decltype (auto) in modern C++? Here are some simple examples that shows difference between auto and decltype(auto), In C++14 and above, we can use decltype(auto) with const int values as below,   const int x = 4096; auto xa = x;    // xa : int decltype(auto) xb = x;  // xb : const int   In C++14 and above, we can use decltype(auto) with int& values as below,   int y = 2048; int& y0 = y;  // y_ : int auto ya = y0;  // yc2 : int decltype(auto) yb = y0;  // yb : int&   In C++14 and above, we can use decltype(auto) with int values as below,   int&& z = 1024; auto zm = std::move(z);   // zm : int decltype(auto) zm2 = std::move(z);  // zm2 : int&&   In C++11 and above, we can use auto for return types,   auto myf(const int& i) { return i; // auto return type : int }   In C++14 and above, we can use decltype(auto) for return types,   decltype(auto) myf2(const int& i) {    return i; // decltype(auto) return type : const int& }   Is there a full example about decltype (auto) in modern C++? Here is a full example that shows how you can use auto and decltype(auto) in different int types. 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 43 44 45 46 47 48 49 50 51 52 53 54   #include   auto myf(const int& i) { return i; // auto […]

The C++14 standard (and later), brings a lot of useful smart pointers and improvements on them. They help us to avoid the mistake of incorrectly freeing the memory addressed by pointers. In modern C++, we have the new and delete operators that are used to allocate and free objects from memory, and in this post, we explain how to use new and delete operators. Can we use new and delete elisions in modern C++ or is it obsolete? Allocating memory and freeing it safely is hard if you are programming a very big application. In Modern C++, there are smart pointers that help avoid the mistake of incorrectly freeing the memory addressed by pointers. Smart pointers make it easy to define pointers, they came with C++11. The most used types of C++ smart pointer are unique_ptr, auto_ptr, shared_ptr, and weak_ptr. Smart pointers are preferable to raw pointers in many different scenarios, but there is still a lot of need to use for the new and delete methods in C++14 and above. When we develop code that requires in-place construction, we need to use new and, possibly, delete operations. They are useful, in a memory pool, as an allocator, as a tagged variant, as a buffer, or as a binary message to a buffer. Sometimes we can use new and delete for some containers if we want to use raw pointers for storage. Modern C++ has a lot of modern choices for faster and safer memory operations. Generally, developers choose to use unique_ptr/make_unique and make_shared rather than raw calls to new and delete. Even though we have a lot of standard smart pointers and abilities, we still need new and/or delete operators. How can we use new and delete elisions in C++? What is the new operator in C++? The new operator in C++, denotes a request for memory allocation on the free memory. If there is sufficient memory, a new operator initializes the memory and returns the address of the newly allocated and initialized memory to the pointer variable.    = new ;   Here, the data_type could be any built-in data type, i.e. basic C / C++ types, array, or any class types i.e. class, structure, union.  Now, let’s see how we can use new operator. We can simply use auto and new to create a new pointer and space for its buffer as below,   auto *ptr = new long int;     or in old style still you can use its type in definition instead of auto as below,   long int *ptr = new long int;     one of the great feature of pointers is we don’t need to allocate them at the beginning, we can set them NULL, and we can allocate them in some steps as below,   long int *ptr = NULL; … ptr = new long int;     What is the delete operator in C++? The delete operator in C++ is used to free the dynamically allocated array pointed by pointer variable. Here is the syntax for the delete operator,   delete ;   we can use delete[] for the pointer_arrays, here is the syntax for them,   delete[] ;   here is how we can use delete to delete a pointer, and this is how we can delete pointer arrays,   int *arr […]

Allocating memory and freeing it safely is hard if you are programming a very big application. In Modern C++ there are smart pointers that help avoid the mistake of incorrectly freeing the memory addressed by pointers. Smart pointers make it easier to define and manage pointers, they came with C++11. The most used types of C++ smart pointer are unique_ptr, auto_ptr, shared_ptr, and weak_ptr. In C++14, there is make_unique (std::make_unique) that can be used to allocate memory for the unique_ptr smart pointers. What is a smart pointer and what is unique_ptr in C++? In computer science, all data and operations during runtime are stored in the memory of our computation machines (computers, IoTs, or other microdevices). This memory is generally RAM (Random Access Memory) that allows data items to be read or written in almost the same amount of time, irrespective of the physical location of data inside the memory. Allocating memory and freeing it safely is really hard if you are programming a very big application. C and C++ were notorious for making this problem even more difficult since earlier coding styles and C++ standards had fewer ways of helping developers deal with pointers and it was fairly easy to make a mistake of manipulating a pointer which had become invalid. In Modern C++, there are smart pointers that help avoid the mistake of incorrectly freeing the memory addressed by pointers which was often the source of bugs in code which could often be difficult to track down. Smart pointers make it easier to manage pointers, they came with the release of the C++11 standard. The most used types of C++ smart pointer are unique_ptr, auto_ptr, shared_ptr, and weak_ptr. std::unique_ptr is a smart pointer that manages and owns another object with a pointer, when the unique_ptr goes out of scope C++ disposes of that object automatically. If you want to do some magic in memory operations use std::unique_ptr. Here are more details on how you can use unique_ptr in C++, What is std::make_unique in C++? The std::make_unique is a new feature that comes with C++14. It is used to allocate memory for the unique_ptr smart pointers, thus managing the lifetime of dynamically allocated objects. std::make_unique template constructs an array of the given dynamic size in memory, and these array elements are value-initialized. Since C++14 to C++20, the std::make_unique function is declared as a template as below,   template unique_ptr make_unique( std::size_t size );     template unique_ptr make_unique( Args&&… args );   The std::make_unique function does not have an allocator-aware counterpart; it returns unique_ptr which would contain an allocator object and invoke both destroy and deallocate in its operator(). How to use std::make_unique with std::unique_ptr in C++? Let’s assume you have a simple class named myclass, We can create a unique pointer (a smart pointer) with this class as below,   std::unique_ptr p = std::make_unique();   Or it can be used with struct as below:   struct st_xy {     int x,y; };   We can create a unique pointer as we illustrate in the example below.   std::unique_ptr xy = std::make_unique();   We can use the auto keyword and we can define the maximum array elements like so:   auto ui = std::make_unique(5);   What are the advantages to use std::make_unique in C++? The std::make_unique function is useful when allocating smart pointer, because: We don’t need to think about new/delete or new[]/delete[] elisions. When […]

C++ is a very precise programming language that allows you to use memory operations in a wide variety of ways. Mastering efficient memory handling will improve your app performance at run time and can result in faster applications that have optimal memory usage. One of the many useful features that come with the C++14 standard is the std::exchange algorithm that is defined in the utility header. In this post, we explain how to use std::exchange in C++. What is std::exchange in C++? The std::exchange algorithm is defined in the header and it is a built-in function that comes with C++14. The std::exchange algorithm copies the new value to a given object and it will return the old value of that object. Here is the template definition syntax (since C++14, until C++20):   template T exchange( T& object, U&& new_value );   How to use std::exchange in C++? We can use std::exchange to exchange variables values as below, and we can obtain old value from the return value of std::exchange.   int x = 500; int y = std::exchange(x, 333);   After these lines, x is now 333 and y is the old value of x , 500. We can use std::exchange to set values of object lists (i.e vectors) as shown below:   std::vector vec; std::exchange( vec, { 10, 20, 30, 40, 50 } );   In addition, we can copy old values to another object list as we show in the following example:   std::vector vec, vec0; vec0 = std::exchange( vec, { 10, 20, 30, 40, 50 } );   We can use std::exchange to change function definitions too, for example assume we have myf1() function, now we want to exchange myf() function to myf1() function, this is how we can do:   void (*myf)(); std::exchange(myf, myf1); // myf is now myf1 myf();   Is there a full example of how to use std::exchange in C++? Here is a full example of how to use std::exchange in C++. 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 43 44 45 46   #include #include   void myf1() { std::cout