Re: [PATCH] streambuf_iterator: avoid debug-dependent behaviour

[Jonathan Wakely]

On 28/09/17 11:50 +0100, Jonathan Wakely wrote:

On 21/09/17 07:46 +0200, François Dumont wrote:

Gentle reminder, ok to commit ?


No. Could you and Petr please come to an agreement about what is
actually wrong with the current implementation, and agree on a
solution?

Currently you're both just proposing patches that do different things,
without indicating why one patch is better than the other.

I understand that we want to remove the debugmode-dependent behaviour,
but I'd like to see any other changes justified by references to the
standard.


Here's a test we currently fail, but it looks like we should pass it:
http://llvm.org/svn/llvm-project/libcxx/trunk/test/std/iterators/stream.iterators/istreambuf.iterator/istreambuf.iterator.cons/proxy.pass.cpp

Do the changes either of you is proposing change this result?

Re: [PATCH] streambuf_iterator: avoid debug-dependent behaviour

[Jonathan Wakely]

On 21/09/17 07:46 +0200, François Dumont wrote:

Gentle reminder, ok to commit ?


No. Could you and Petr please come to an agreement about what is
actually wrong with the current implementation, and agree on a
solution?

Currently you're both just proposing patches that do different things,
without indicating why one patch is better than the other.

I understand that we want to remove the debugmode-dependent behaviour,
but I'd like to see any other changes justified by references to the
standard.


diff --git a/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/2.cc 
b/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/2.cc
index b81f4d4..e3d99f9 100644
--- a/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/2.cc
+++ b/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/2.cc
@@ -25,9 +25,7 @@

void test02(void)
{
-
  typedef std::istreambuf_iterator cistreambuf_iter;
-  typedef cistreambuf_iter::streambuf_type cstreambuf_type;
  const char slit01[] = "playa hermosa, liberia, guanacaste";
  std::string str01(slit01);
  std::istringstream istrs00(str01);
@@ -35,10 +33,17 @@ void test02(void)

  // ctor sanity checks
  cistreambuf_iter istrb_it01(istrs00);
-  cistreambuf_iter istrb_it02;
-  std::string tmp(istrb_it01, istrb_it02); 
+  cistreambuf_iter istrb_eos;

+  VERIFY( istrb_it01 != istrb_eos );
+
+  std::string tmp(istrb_it01, istrb_eos);
  VERIFY( tmp == str01 );

+  VERIFY( istrb_it01 != istrb_eos );


Why should this condition be true? The std::string constructor
increments the iterator until it reaches the end-of-stream value.

This is true with our current implementation, but that seems like a
bug, not something we want to verify in the testsuite.


+  cistreambuf_iter old = istrb_it01++;
+  VERIFY( old == istrb_eos );


This behaviour makes no sense.


+  VERIFY( istrb_it01 == istrb_eos );
+
  cistreambuf_iter istrb_it03(0);
  cistreambuf_iter istrb_it04;
  VERIFY( istrb_it03 == istrb_it04 );

Re: [PATCH] streambuf_iterator: avoid debug-dependent behaviour

[François Dumont]

Gentle reminder, ok to commit ?

* include/bits/streambuf_iterator.h
(istreambuf_iterator<>(const istreambuf_iterator&)): Remove useless
noexcept qualificatio::operator*()): Do not capture iterator state
in Debug assertion.
(istreambuf_iterator<>::operator++()): Likewise.
(istreambuf_iterator<>::operator++(int)): Likewise.
(istreambuf_iterator<>::_M_get()): Simplify implementation.
(istreambuf_iterator<>::_S_at_eof()): New.
(istreambuf_iterator<>::_M_at_eof()): Adapt, use latter.
(find(istreambuf_iterator<>, istreambuf_iterator<>, _CharT)):
Return an iterator with _M_c set to eof to capture streambuf state
on evaluation.
(testsuite/24_iterators/istreambuf_iterator/2.cc): Add checks.

François

On 09/09/2017 22:16, François Dumont wrote:

Hi

Completing the execution of tests revealed a lot about the current 
implementation.


The main point of current implementation is to delay as much as 
possible the capture of the current streambuf position. So my original 
proposal capturing state on instantiation was wrong.


This new proposal concentrate on the debug-dependent code. Debug 
assertions now avoids calling _M_at_eof() which also capture iterator 
state. It also simplifies _M_get() method a little bit like Petr 
proposed but keeping the _M_sbuf reset when reaching eof. Thanks to 
this work I realized that std::find specialization could also be 
simplified by returning a streambuf_iterator which will capture 
current streambuf state on evaluation.


 Note that I haven't been able to create a test case revealing the 
problem. This is more a code quality issue as current code violates 
the principal that debug asserts shouldn't impact object state. AFAIK 
this is noticeable only under gdb.


Regarding avoiding the reset of _M_sbuf it might be possible,your 
test case could be a good reason to do so. But this is going to be a 
big change for current implementation so don't forget to run all 
testsuite and to consider the std::copy and std::find specializations.


Tested under Linux x86_64, normal and debug modes.

Ok to commit ?

François


On 08/09/2017 07:47, Petr Ovtchenkov wrote:

-gcc-patches

On Thu, 7 Sep 2017 23:02:15 +0200
François Dumont  wrote:


+_M_c = _M_sbuf->sgetc();
+if (_S_at_eof(_M_c))
+  _M_sbuf = 0;

_M_sbuf = 0; <--- Is not what I axpect here.

Suggestions will be later, after we finish copyright assignment for
changes procedure (in progress).

WBR,

--

- ptr





diff --git a/libstdc++-v3/include/bits/streambuf_iterator.h b/libstdc++-v3/include/bits/streambuf_iterator.h
index f0451b1..ad9c89f 100644
--- a/libstdc++-v3/include/bits/streambuf_iterator.h
+++ b/libstdc++-v3/include/bits/streambuf_iterator.h
@@ -103,7 +103,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   : _M_sbuf(0), _M_c(traits_type::eof()) { }
 
 #if __cplusplus >= 201103L
-  istreambuf_iterator(const istreambuf_iterator&) noexcept = default;
+  istreambuf_iterator(const istreambuf_iterator&) = default;
 
   ~istreambuf_iterator() = default;
 #endif
@@ -122,28 +122,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   char_type
   operator*() const
   {
+	int_type __c = _M_get();
+
 #ifdef _GLIBCXX_DEBUG_PEDANTIC
 	// Dereferencing a past-the-end istreambuf_iterator is a
 	// libstdc++ extension
-	__glibcxx_requires_cond(!_M_at_eof(),
+	__glibcxx_requires_cond(!_S_at_eof(__c),
 _M_message(__gnu_debug::__msg_deref_istreambuf)
 ._M_iterator(*this));
 #endif
-	return traits_type::to_char_type(_M_get());
+	return traits_type::to_char_type(__c);
   }
 
   /// Advance the iterator.  Calls streambuf.sbumpc().
   istreambuf_iterator&
   operator++()
   {
-	__glibcxx_requires_cond(!_M_at_eof(),
+	__glibcxx_requires_cond(_M_sbuf
+			&& (!_S_at_eof(_M_c) || !_S_at_eof(_M_sbuf->sgetc())),
 _M_message(__gnu_debug::__msg_inc_istreambuf)
 ._M_iterator(*this));
-	if (_M_sbuf)
-	  {
+
 	_M_sbuf->sbumpc();
 	_M_c = traits_type::eof();
-	  }
 	return *this;
   }
 
@@ -151,16 +152,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   istreambuf_iterator
   operator++(int)
   {
-	__glibcxx_requires_cond(!_M_at_eof(),
+	__glibcxx_requires_cond(_M_sbuf
+			&& (!_S_at_eof(_M_c) || !_S_at_eof(_M_sbuf->sgetc())),
 _M_message(__gnu_debug::__msg_inc_istreambuf)
 ._M_iterator(*this));
 
 	istreambuf_iterator __old = *this;
-	if (_M_sbuf)
-	  {
 	__old._M_c = _M_sbuf->sbumpc();
 	_M_c = traits_type::eof();
-	  }
 	return __old;
   }
 
@@ -176,26 +175,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   int_type
   _M_get() const
   {
-	const int_type __eof = traits_type::eof();
-	int_type __ret = __eof;
-	if (_M_sbuf)
-	  {
-	if (!traits_type::eq_int_type(_M_c, __eof))
-	  __ret = _M_c;
-	else if (!traits_type::eq_int_type((__ret = _M_sbuf->sgetc()),
-	   __eof))
-	  _M_c = __ret;
-	else
+	if (_M_sbuf && _S_at_eof(_M_c) && _S_at_eof(_M_c = 

Re: [PATCH] streambuf_iterator: avoid debug-dependent behaviour

[François Dumont]

Hi

Completing the execution of tests revealed a lot about the current 
implementation.


The main point of current implementation is to delay as much as 
possible the capture of the current streambuf position. So my original 
proposal capturing state on instantiation was wrong.


This new proposal concentrate on the debug-dependent code. Debug 
assertions now avoids calling _M_at_eof() which also capture iterator 
state. It also simplifies _M_get() method a little bit like Petr 
proposed but keeping the _M_sbuf reset when reaching eof. Thanks to this 
work I realized that std::find specialization could also be simplified 
by returning a streambuf_iterator which will capture current streambuf 
state on evaluation.


 Note that I haven't been able to create a test case revealing the 
problem. This is more a code quality issue as current code violates the 
principal that debug asserts shouldn't impact object state. AFAIK this 
is noticeable only under gdb.


Regarding avoiding the reset of _M_sbuf it might be possible,your 
test case could be a good reason to do so. But this is going to be a big 
change for current implementation so don't forget to run all testsuite 
and to consider the std::copy and std::find specializations.


Tested under Linux x86_64, normal and debug modes.

Ok to commit ?

François


On 08/09/2017 07:47, Petr Ovtchenkov wrote:

-gcc-patches

On Thu, 7 Sep 2017 23:02:15 +0200
François Dumont  wrote:


+   _M_c = _M_sbuf->sgetc();
+   if (_S_at_eof(_M_c))
+ _M_sbuf = 0;

_M_sbuf = 0; <--- Is not what I axpect here.

Suggestions will be later, after we finish copyright assignment for
changes procedure (in progress).

WBR,

--

- ptr



diff --git a/libstdc++-v3/include/bits/streambuf_iterator.h b/libstdc++-v3/include/bits/streambuf_iterator.h
index f0451b1..ad9c89f 100644
--- a/libstdc++-v3/include/bits/streambuf_iterator.h
+++ b/libstdc++-v3/include/bits/streambuf_iterator.h
@@ -103,7 +103,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   : _M_sbuf(0), _M_c(traits_type::eof()) { }
 
 #if __cplusplus >= 201103L
-  istreambuf_iterator(const istreambuf_iterator&) noexcept = default;
+  istreambuf_iterator(const istreambuf_iterator&) = default;
 
   ~istreambuf_iterator() = default;
 #endif
@@ -122,28 +122,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   char_type
   operator*() const
   {
+	int_type __c = _M_get();
+
 #ifdef _GLIBCXX_DEBUG_PEDANTIC
 	// Dereferencing a past-the-end istreambuf_iterator is a
 	// libstdc++ extension
-	__glibcxx_requires_cond(!_M_at_eof(),
+	__glibcxx_requires_cond(!_S_at_eof(__c),
 _M_message(__gnu_debug::__msg_deref_istreambuf)
 ._M_iterator(*this));
 #endif
-	return traits_type::to_char_type(_M_get());
+	return traits_type::to_char_type(__c);
   }
 
   /// Advance the iterator.  Calls streambuf.sbumpc().
   istreambuf_iterator&
   operator++()
   {
-	__glibcxx_requires_cond(!_M_at_eof(),
+	__glibcxx_requires_cond(_M_sbuf
+			&& (!_S_at_eof(_M_c) || !_S_at_eof(_M_sbuf->sgetc())),
 _M_message(__gnu_debug::__msg_inc_istreambuf)
 ._M_iterator(*this));
-	if (_M_sbuf)
-	  {
+
 	_M_sbuf->sbumpc();
 	_M_c = traits_type::eof();
-	  }
 	return *this;
   }
 
@@ -151,16 +152,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   istreambuf_iterator
   operator++(int)
   {
-	__glibcxx_requires_cond(!_M_at_eof(),
+	__glibcxx_requires_cond(_M_sbuf
+			&& (!_S_at_eof(_M_c) || !_S_at_eof(_M_sbuf->sgetc())),
 _M_message(__gnu_debug::__msg_inc_istreambuf)
 ._M_iterator(*this));
 
 	istreambuf_iterator __old = *this;
-	if (_M_sbuf)
-	  {
 	__old._M_c = _M_sbuf->sbumpc();
 	_M_c = traits_type::eof();
-	  }
 	return __old;
   }
 
@@ -176,26 +175,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   int_type
   _M_get() const
   {
-	const int_type __eof = traits_type::eof();
-	int_type __ret = __eof;
-	if (_M_sbuf)
-	  {
-	if (!traits_type::eq_int_type(_M_c, __eof))
-	  __ret = _M_c;
-	else if (!traits_type::eq_int_type((__ret = _M_sbuf->sgetc()),
-	   __eof))
-	  _M_c = __ret;
-	else
+	if (_M_sbuf && _S_at_eof(_M_c) && _S_at_eof(_M_c = _M_sbuf->sgetc()))
 	  _M_sbuf = 0;
-	  }
-	return __ret;
+	return _M_c;
   }
 
   bool
   _M_at_eof() const
+  { return _S_at_eof(_M_get()); }
+
+  static bool
+  _S_at_eof(int_type __c)
   {
 	const int_type __eof = traits_type::eof();
-	return traits_type::eq_int_type(_M_get(), __eof);
+	return traits_type::eq_int_type(__c, __eof);
   }
 };
 
@@ -373,13 +366,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   typedef typename __is_iterator_type::traits_type traits_type;
   typedef typename __is_iterator_type::streambuf_type  streambuf_type;
   typedef typename traits_type::int_type   int_type;
+  const int_type __eof = traits_type::eof();
 
   if (__first._M_sbuf && !__last._M_sbuf)
 	{
 	  const int_type __ival = 

Re: [PATCH] streambuf_iterator: avoid debug-dependent behaviour

[Petr Ovtchenkov]

-gcc-patches 

On Thu, 7 Sep 2017 23:02:15 +0200
François Dumont  wrote:

> + _M_c = _M_sbuf->sgetc();
> + if (_S_at_eof(_M_c))
> +   _M_sbuf = 0;

_M_sbuf = 0; <--- Is not what I axpect here.

Suggestions will be later, after we finish copyright assignment for
changes procedure (in progress).

WBR,

--

   - ptr

Re: [PATCH] streambuf_iterator: avoid debug-dependent behaviour

[François Dumont]

Hi

Following this report I had a closer look to this debug-dependent 
behavior which I agree about.


I have added some checks to 2.cc as shown in the patch. Initially the 
test was failing because:
/home/fdt/dev/gcc/git/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/2.cc:45: 
void test02(): Assertion 'old != istrb_eos' failed.


This was coming from the __old._M_c = _M_sbuf->sbumpc() line in the 
post-increment operator. The post-increment is supposed to return a copy 
of the current iterator which this assignment is compromising. So I try 
to remove the assignment and test failed later:


/home/fdt/dev/gcc/git/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/2.cc:104: 
void test02(): Assertion 'c == slit01[i]' failed.


However, run in debug mode, it worked fine.

The test is failing in normal mode because the iterator instantiation 
doesn't read the streambuf and without the previous __old._M_c 
assignment _M_c is still pointing to eos. In debug mode, _M_at_eof() 
initialize the iterator and so it work nicely.


So for those reasons I would like to propose attached patch. 
Additionally it gets rid of the mutable usage. And I also remove a 
useless noexcept qualification on the defaulted copy constructor.


François

On 01/09/2017 11:10, Jonathan Wakely wrote:

On 24/08/17 12:57 +0300, Petr Ovtchenkov wrote:

Explicit do sgetc from associated streambuf. Avoid debug-dependent
sgetc (within _M_at_eof()):

  __glibcxx_requires_cond(!_M_at_eof(),
_M_message(__gnu_debug::__msg_inc_istreambuf)
  ._M_iterator(*this));

Increment operators not require not-eof precoditions.

Don't unlink associated streambuf if eof detected (in _M_get).

Clean logic in postfix increment operator.


I find it very hard to understand the reasons for this patch. What
you've written above is too terse for me.

Are you fixing a bug? If so, do you have a testcase that demonstrates
the problem, and is fixed by these changes?

Is this just refactoring, without changing behaviour?

Finally, and very importantly, do you have a copyright assignment for
changes to GCC? See https://gcc.gnu.org/contribute.html#legal





diff --git a/libstdc++-v3/include/bits/streambuf_iterator.h b/libstdc++-v3/include/bits/streambuf_iterator.h
index f0451b1..27d0725 100644
--- a/libstdc++-v3/include/bits/streambuf_iterator.h
+++ b/libstdc++-v3/include/bits/streambuf_iterator.h
@@ -94,8 +94,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // the "end of stream" iterator value.
   // NB: This implementation assumes the "end of stream" value
   // is EOF, or -1.
-  mutable streambuf_type*	_M_sbuf;
-  mutable int_type		_M_c;
+  streambuf_type*	_M_sbuf;
+  int_type		_M_c;
 
 public:
   ///  Construct end of input stream iterator.
@@ -103,18 +103,26 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   : _M_sbuf(0), _M_c(traits_type::eof()) { }
 
 #if __cplusplus >= 201103L
-  istreambuf_iterator(const istreambuf_iterator&) noexcept = default;
+  istreambuf_iterator(const istreambuf_iterator&) = default;
 
   ~istreambuf_iterator() = default;
 #endif
 
   ///  Construct start of input stream iterator.
   istreambuf_iterator(istream_type& __s) _GLIBCXX_USE_NOEXCEPT
-  : _M_sbuf(__s.rdbuf()), _M_c(traits_type::eof()) { }
+  : _M_sbuf(__s.rdbuf()), _M_c(traits_type::eof())
+  {
+	if (_M_sbuf)
+	  _M_get();
+  }
 
   ///  Construct start of streambuf iterator.
   istreambuf_iterator(streambuf_type* __s) _GLIBCXX_USE_NOEXCEPT
-  : _M_sbuf(__s), _M_c(traits_type::eof()) { }
+  : _M_sbuf(__s), _M_c(traits_type::eof())
+  {
+	if (_M_sbuf)
+	  _M_get();
+  }
 
   ///  Return the current character pointed to by iterator.  This returns
   ///  streambuf.sgetc().  It cannot be assigned.  NB: The result of
@@ -122,28 +130,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   char_type
   operator*() const
   {
+	int_type __c = _M_get();
+
 #ifdef _GLIBCXX_DEBUG_PEDANTIC
 	// Dereferencing a past-the-end istreambuf_iterator is a
 	// libstdc++ extension
-	__glibcxx_requires_cond(!_M_at_eof(),
+	__glibcxx_requires_cond(!_S_at_eof(__c),
 _M_message(__gnu_debug::__msg_deref_istreambuf)
 ._M_iterator(*this));
 #endif
-	return traits_type::to_char_type(_M_get());
+	return traits_type::to_char_type(__c);
   }
 
   /// Advance the iterator.  Calls streambuf.sbumpc().
   istreambuf_iterator&
   operator++()
   {
-	__glibcxx_requires_cond(!_M_at_eof(),
+	__glibcxx_requires_cond(_M_sbuf,
 _M_message(__gnu_debug::__msg_inc_istreambuf)
 ._M_iterator(*this));
-	if (_M_sbuf)
-	  {
-	_M_sbuf->sbumpc();
-	_M_c = traits_type::eof();
-	  }
+	_M_sbuf->sbumpc();
+	_M_get();
 	return *this;
   }
 
@@ -151,16 +158,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   istreambuf_iterator
   operator++(int)
   {
-	__glibcxx_requires_cond(!_M_at_eof(),
-_M_message(__gnu_debug::__msg_inc_istreambuf)
-

Re: [PATCH] streambuf_iterator: avoid debug-dependent behaviour

[Jonathan Wakely]

On 24/08/17 12:57 +0300, Petr Ovtchenkov wrote:

Explicit do sgetc from associated streambuf. Avoid debug-dependent
sgetc (within _M_at_eof()):

  __glibcxx_requires_cond(!_M_at_eof(),
  _M_message(__gnu_debug::__msg_inc_istreambuf)
  ._M_iterator(*this));

Increment operators not require not-eof precoditions.

Don't unlink associated streambuf if eof detected (in _M_get).

Clean logic in postfix increment operator.


I find it very hard to understand the reasons for this patch. What
you've written above is too terse for me.

Are you fixing a bug? If so, do you have a testcase that demonstrates
the problem, and is fixed by these changes?

Is this just refactoring, without changing behaviour?

Finally, and very importantly, do you have a copyright assignment for
changes to GCC? See https://gcc.gnu.org/contribute.html#legal

[PATCH] streambuf_iterator: avoid debug-dependent behaviour

[Petr Ovtchenkov]

Explicit do sgetc from associated streambuf. Avoid debug-dependent
sgetc (within _M_at_eof()):

   __glibcxx_requires_cond(!_M_at_eof(),
   _M_message(__gnu_debug::__msg_inc_istreambuf)
   ._M_iterator(*this));

Increment operators not require not-eof precoditions.

Don't unlink associated streambuf if eof detected (in _M_get).

Clean logic in postfix increment operator.
---
 libstdc++-v3/include/bits/streambuf_iterator.h | 24 +---
 1 file changed, 5 insertions(+), 19 deletions(-)

diff --git a/libstdc++-v3/include/bits/streambuf_iterator.h 
b/libstdc++-v3/include/bits/streambuf_iterator.h
index 2230e94..cff3b69 100644
--- a/libstdc++-v3/include/bits/streambuf_iterator.h
+++ b/libstdc++-v3/include/bits/streambuf_iterator.h
@@ -136,9 +136,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   istreambuf_iterator&
   operator++()
   {
-   __glibcxx_requires_cond(!_M_at_eof(),
-   _M_message(__gnu_debug::__msg_inc_istreambuf)
-   ._M_iterator(*this));
if (_M_sbuf)
  {
_M_sbuf->sbumpc();
@@ -151,14 +148,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   istreambuf_iterator
   operator++(int)
   {
-   __glibcxx_requires_cond(!_M_at_eof(),
-   _M_message(__gnu_debug::__msg_inc_istreambuf)
-   ._M_iterator(*this));
+_M_get();
 
istreambuf_iterator __old = *this;
if (_M_sbuf)
  {
-   __old._M_c = _M_sbuf->sbumpc();
+   _M_sbuf->sbumpc();
_M_c = traits_type::eof();
  }
return __old;
@@ -177,18 +172,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   _M_get() const
   {
const int_type __eof = traits_type::eof();
-   int_type __ret = __eof;
-   if (_M_sbuf)
- {
-   if (!traits_type::eq_int_type(_M_c, __eof))
- __ret = _M_c;
-   else if (!traits_type::eq_int_type((__ret = _M_sbuf->sgetc()),
-  __eof))
- _M_c = __ret;
-   else
- _M_sbuf = 0;
- }
-   return __ret;
+   if (_M_sbuf && traits_type::eq_int_type(_M_c, __eof))
+  _M_c = _M_sbuf->sgetc();
+   return _M_c;
   }
 
   bool
-- 
2.10.1