This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of New status.

2504. basic_streambuf is not an abstract class

Section: 27.6.3 [streambuf] Status: New Submitter: Jonathan Wakely Opened: 2015-05-28 Last modified: 2015-08-17

Priority: 3

View all other issues in [streambuf].

View all issues with New status.

Discussion:

27.6.3 [streambuf] p1 says:

The class template basic_streambuf<charT, traits> serves as an abstract base class for deriving various stream buffers whose objects each control two character sequences: […]

The term "abstract base class" is not defined in the standard, but "abstract class" is (10.6.3 [class.abstract]).

According to the synopsis basic_streambuf has no pure virtual functions so is not an abstract class and none of libstdc++, libc++, or dinkumware implement it as an abstract class. I don't believe the wording was ever intended to require it to be an abstract class, but it could be read that way.

I suggest the wording be changed to "polymorphic base class" or something else that can't be seen to imply a normative requirement to make it an abstract class.

Proposed resolution: