Other Smaller Removed or Deprecated Items

Deprecated Features

Deprecating shared_ptr::unique()

In C++14 shared_ptr::unique() was defined as use_count() == 1. But since use_count() is only approximation in multithreaded environments (as it doesn’t imply any synchronisation access) then unique() it not reliable.

See more information in P0521.

Deprecating <codecvt>

The <codecvt> header declares several conversion utilities: codecvt_utf8, codecvt_utf16 and codecvt_utf8_utf16. But those classes are hard to use, unsafe and not well specified.

Note: the class std::codesvt is not deprecated, as it’s located in another header <locale>. So you can still use that.

See more information in P0618R0

Removing Deprecated Iostreams Aliases

Since C++11 the following iostream types and methods were deprecated, and now they are removed from the Library.

typedef T1 io_state;  // T1 is integer
typedef T2 open_mode; // T2 is integer
typedef T3 seek_dir;  // T3 is integer
typedef implementation-defined streamoff;
typedef implementation-defined streampos;
basic_streambuf::stossc()

Also, the methods and overrides that depend on the above types were removed.

Previously they were all declared in Annex D of the Standard: [depr.ios.members].

See more information in P0004R1.

Deprecate C library headers

The following headers are now deprecated:

• <ccomplex>
• <cstdalign>
• <cstdbool>
• <ctgmath>

This is a result of cleaning up places that depend on the C99 specification. In C++17 the Standard relates to C11 rather than C99.

See more information in P0063R3.

Deprecate std::result_of

The type trait std::result_of used a non-variadic template declaration which limited its uses. It’s advised to use enhanced traits, for example std::invoke_result.

See more information in P0604R0.

Deprecate std::memory_order_consume Temporarily

The memory model of memory_order_consume is hard to implement and not well specified in the Standard. The model is now temporarily deprecated and may reappear in the future.

See more information in P0371R1.

Remove allocator support from std::function

std::function uses type-erasure to handle callable objects. It’s very complicated (or not implementable efficiently) to have allocator support for this type, so it was decided to remove this from the Standard.

See more information in P0302R1.