title: "Welcome back to C++ (Modern C++)"

ms.date: "11/19/2019"

Over the past 25 years, C++ has been one of the most widely used programming languages in the world. Well-written C++ programs are fast and efficient. The language is more flexible than other languages because it enables you to access low-level hardware features to maximize speed and minimize memory requirements. You can use it to create a wide range of apps—from games, to high-performance scientific software, device drivers, embedded programs, libraries and compilers for other programming languages, Windows client apps, and much more.

One of the original requirements for C++ was backward compatibility with the C language. As a result C++ has always permitted C-style programming with raw pointers, arrays, null-terminated character strings, custom data structures, and other features that may enable great performance but can also spawn bugs and complexity. The evolution of C++ has emphasized features that greatly reduce the need to use C-style idioms. The old C-programming facilities are there when you need them, but with modern C++ code you should need them less and less. Modern C++ code is simpler, safer, more elegant, and still as fast as ever.

One of the major classes of bugs in C-style programming is the *memory leak* due to failure to call **delete** for memory that was allocated with **new**. Modern C++ emphasizes the principle of *resource acquisition is initialization* which states that any resource (heap memory, file handles, sockets, and so on) should be *owned* by an object that creates, or receives, the newly-allocated resource in its constructor, and deletes it in its destructor. By adhering to the principle of RAII, you guarantee that all resources will be properly returned to the operating system when the owning object goes out of scope. To support easy adoption of RAII principles, the C++ Standard Library provides three smart pointer types: [std::unique_ptr](../standard-library/unique-ptr-class.md), [std::shared_ptr](../standard-library/shared-ptr-class.md), and [std::weak_ptr](../standard-library/weak-ptr-class.md). A smart pointer handles the allocation and deletion of the memory it owns. The following example shows a class with an array member that is allocated on the heap in the call to `make_unique()`. The calls to **new** and **delete** are encapsulated by the `unique_ptr` class. When a `widget` object goes out of scope, the unique_ptr destructor will be invoked and it will release the memory that was allocated for the array.

C-style strings are another major source of bugs. By using [std::string and std::wstring](../standard-library/basic-string-class.md) you can eliminate virtually all the errors associated with C-style strings, and gain the benefit of member functions for searching, appending, prepending, and so on. Both are highly optimized for speed. When passing a string to a function that requires only read-only access, in C++17 you can use [std::string_view](../standard-library/basic-string-view-class.md) for even greater performance benefit.

The Standard Library containers all follow the principle of RAII, provide iterators for safe traversal of elements, are highly optimized for performance and have been thoroughly tested for correctness. By using these containers whenever possible, you eliminate the potential for bugs or inefficiencies that might be introduced in custom data structures. By default, use [vector](../standard-library/vector-class.md) as the preferred sequential container in C++. This is equivalent to `List<T>` in .NET languages.

- **for_each**, the default traversal algorithm (along with range-based for loops).

C-style iteration over arrays and containers is prone to indexing errors and is also tedious to type. To eliminate these errors, and make your code more readable, use range-based for loops with Standard Library containers as well as raw arrays. For more information, see [Range-based for statement](../cpp/range-based-for-statement-cpp.md).

Macros in C and C++ are tokens that are processed by the preprocessor prior to compilation. Each instance of a macro token is replaced with its defined value or expression before the file is compiled. Macros are commonly used in C-style programming to define compile-time constant values. However, macros are error-prone and difficult to debug. In modern C++, you should prefer [constexpr](constexpr-cpp.md) variables for compile-time constants:

Modern C++ provides *move semantics* which make it possible to eliminate unnecessary memory copies which in earlier versions of the language were unavoidable in certain situations. A *move* operation transfers ownership of a resource from one object to the next without making a copy. When implementing a class that owns a resource such as heap memory, file handles, and so on, you can define a *move constructor* and *move assignment operator* for it. The compiler will choose these special members during overload resolution in situations where a copy is not needed. The Standard Library container types invoke the move constructor on objects if one is defined. For more information, see [Move Constructors and Move Assignment Operators (C++)](move-constructors-and-move-assignment-operators-cpp.md).

In C-style programming, a function can be passed to another function by means of a *function pointer*. Function pointers are inconvenient to maintain and understand because the function they refer to may be defined elsewhere in the source code, far away from the point at which it is being invoked. Also, they are not type-safe. Modern C++ provides function objects, classes that override the [()](function-call-operator-parens.md) operator which enables them to be called like a function. The most convenient way to create function objects is with inline [lambda expressions](../cpp/lambda-expressions-in-cpp.md). The following example shows how to use a lambda expression to pass a function object, that the `for_each` function will invoke on each element in the vector: