C++17

History

Removed

• Removal of trigraphs.
• Removal of some deprecated types and functions from the standard library, including std::auto_ptr, std::random_shuffle, and old function adaptors. These were superseded in C++11 by improved facilities such as std::unique_ptr, std::shuffle, std::bind, and lambdas.
• Removal of the use of the keyword as a storage class specifier. This keyword is now reserved and unused.

  New features

Language

• Making the text message for optional
• Allow in a template template parameter
• New rules for Type inference| deduction from braced-init-list
• Nested namespace definitions, e.g., instead of
• Allowing attributes for namespaces and enumerators
• New standard attributes, and
• UTF-8 character literals
• Hexadecimal floating-point literals
• Constant evaluation for all non-type template arguments
• Fold expressions, for variadic templates
• A compile-time static with the form
• Structured binding declarations, allowing
• Initializers in and statements
• copy-initialization and direct-initialization of objects of type from prvalue expressions of type shall result in no copy or move constructors from the prvalue expression. See copy elision for more information.
• Some extensions on over-aligned memory allocation
• Class template argument deduction, introducing constructor deduction guides, eg. allowing instead of requiring explicit constructor arguments types or an additional helper template function.
• Inline variables, which allows the definition of variables in header files without violating the one definition rule. The rules are effectively the same as inline functions
• , allowing the availability of a header to be checked by preprocessor directives
• Value of changed to
• Exception specifications were made part of the function type

  Library

• Most of Library Fundamentals TS I, including:
• *std::string_view, a read-only non-owning reference to a character sequence or string-slice
• * std::optional, for representing optional objects, a data type that may not always be returned by a given algorithm with support for non-return
• * std::any, for holding single values of any type
• std::uncaught_exceptions, as a replacement of std::uncaught_exception in exception handling
• New insertion functions try_emplace and insert_or_assign for std::map and std::unordered_map key-value associative data structures
• Uniform container access: std::size, std::empty and std::data
• Definition of "contiguous iterators"
• A file system library based on boost::filesystem
• Parallel versions of STL algorithms
• Additional mathematical special functions, including elliptic integrals and Bessel functions
• std::variant, a tagged union container
• std::byte, allowing char to be replaced for data types intending to model a byte of data as a byte rather than a character
• Logical operator traits: std::conjunction, std::disjunction and std::negation

  Compiler support

• GCC has had almost complete support for C++17 language features since version 7. Some library features are still not supported.
• Clang 5 and later implement all the features of C++17.
• Visual Studio 2017 15.7 supports almost all of C++17.

  Library support

• libstdc++ since version 9.1 has complete support for c++17
• libc++ as of version 9 has partial support for c++17, with the remainder "in progress"
• MSVC Standard Library since 19.15 complete support for c++17 except for "Elementary String Conversions" and referring to C99 instead of C11.