366. Excessive const-qualification

Section: 31 [input.output] Status: NAD Submitter: Walter Brown, Marc Paterno Opened: 2002-05-10 Last modified: 2016-01-28

Priority: Not Prioritized

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View all issues with NAD status.

Discussion:

The following member functions are declared const, yet return non-const pointers. We believe they are should be changed, because they allow code that may surprise the user. See document N1360 for details and rationale.

[Santa Cruz: the real issue is that we've got const member functions that return pointers to non-const, and N1360 proposes replacing them by overloaded pairs. There isn't a consensus about whether this is a real issue, since we've never said what our constness policy is for iostreams. N1360 relies on a distinction between physical constness and logical constness; that distinction, or those terms, does not appear in the standard.]

Proposed resolution:

In 27.4.4 and 27.4.4.2

Replace

  basic_ostream<charT,traits>* tie() const;

with

  basic_ostream<charT,traits>* tie();
  const basic_ostream<charT,traits>* tie() const;

and replace

  basic_streambuf<charT,traits>* rdbuf() const;

with

  basic_streambuf<charT,traits>* rdbuf();
  const basic_streambuf<charT,traits>* rdbuf() const;

In 27.5.2 and 27.5.2.3.1

Replace

  char_type* eback() const;

with

  char_type* eback();
  const char_type* eback() const;

Replace

  char_type gptr() const;

with

  char_type* gptr();
  const char_type* gptr() const;

Replace

  char_type* egptr() const;

with

  char_type* egptr();
  const char_type* egptr() const;

In 27.5.2 and 27.5.2.3.2

Replace

  char_type* pbase() const;

with

  char_type* pbase();
  const char_type* pbase() const;

Replace

  char_type* pptr() const;

with

  char_type* pptr();
  const char_type* pptr() const;

Replace

  char_type* epptr() const;

with

  char_type* epptr();
  const char_type* epptr() const;

In 27.7.2, 27.7.2.2, 27.7.3 27.7.3.2, 27.7.4, and 27.7.6

Replace

  basic_stringbuf<charT,traits,Allocator>* rdbuf() const;

with

  basic_stringbuf<charT,traits,Allocator>* rdbuf();
  const basic_stringbuf<charT,traits,Allocator>* rdbuf() const;

In 27.8.1.5, 27.8.1.7, 27.8.1.8, 27.8.1.10, 27.8.1.11, and 27.8.1.13

Replace

  basic_filebuf<charT,traits>* rdbuf() const;

with

  basic_filebuf<charT,traits>* rdbuf();
  const basic_filebuf<charT,traits>* rdbuf() const;

Rationale:

The existing specification is a bit sloppy, but there's no particular reason to change this other than tidiness, and there are a number of ways in which streams might have been designed differently if we were starting today. There's no evidence that the existing constness policy is harming users. We might consider a different constness policy as part of a full stream redesign.