[v3] Fix write after read on eof

[Paolo Carlini <pcarlini at unitus dot it>]

Hi,

tested x86-linux, committed.

Paolo.

///////////
2003-06-26  Paolo Carlini  <pcarlini@unitus.it>
            Nathan C. Myers  <ncm-nospam@cantrip.org>

	* include/bits/fstream.tcc (_M_underflow): When the actual
	end of file is reached, set 'uncommitted' mode to allow a
	next write without an intervening seek (see C++98 27.8.1.1,2
	and C89 7.9.5.3).
	* testsuite/27_io/basic_filebuf/underflow/char/2.cc: New.

diff -urN libstdc++-v3-curr/include/bits/fstream.tcc libstdc++-v3/include/bits/fstream.tcc
--- libstdc++-v3-curr/include/bits/fstream.tcc	2003-06-23 21:27:42.000000000 +0200
+++ libstdc++-v3/include/bits/fstream.tcc	2003-06-25 18:43:35.000000000 +0200
@@ -215,7 +215,7 @@
 	    {
 	      char* __buf = static_cast<char*>(__builtin_alloca(__buflen));
 	      __elen = _M_file.xsgetn(__buf, __buflen);
-	      
+ 
 	      const char* __eend;
 	      char_type* __iend;
 	      codecvt_base::result __r;
@@ -246,7 +246,15 @@
 	      __ret = traits_type::to_int_type(*this->gptr());
 	      if (__bump)
 		this->gbump(1);
-	    }	   	    
+	    }
+	  else if (__elen == 0)
+	    {
+	      // If the actual end of file is reached, set 'uncommitted'
+	      // mode, thus allowing an immediate write without an 
+	      // intervening seek.
+	      _M_set_buffer(-1);
+	      _M_reading = false;
+	    }
 	}
       _M_last_overflowed = false;	
       return __ret;
diff -urN libstdc++-v3-curr/testsuite/27_io/basic_filebuf/underflow/char/2.cc libstdc++-v3/testsuite/27_io/basic_filebuf/underflow/char/2.cc
--- libstdc++-v3-curr/testsuite/27_io/basic_filebuf/underflow/char/2.cc	1970-01-01 01:00:00.000000000 +0100
+++ libstdc++-v3/testsuite/27_io/basic_filebuf/underflow/char/2.cc	2003-06-25 19:43:45.000000000 +0200
@@ -0,0 +1,48 @@
+// 2003-06-25 Paolo Carlini <pcarlini@unitus.it>
+
+// Copyright (C) 2003 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 2, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING.  If not, write to the Free
+// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+// USA.
+
+// 27.8.1.4 Overridden virtual functions
+
+#include <fstream>
+#include <testsuite_hooks.h>
+
+void test01()
+{
+  bool test = true;
+  using namespace std;
+
+  filebuf fb_out, fb_in_out;
+  
+  fb_out.open("tmp_underflow.tst", ios::out);
+  fb_out.sputc('S');
+  fb_out.sputc('T');
+  fb_out.close();
+
+  fb_in_out.open("tmp_underflow.tst", ios::in | ios::out);
+  while (fb_in_out.sbumpc() != filebuf::traits_type::eof());
+
+  VERIFY( fb_in_out.sputc('x') == 'x' );
+  fb_in_out.close();
+}
+
+int main()
+{
+  test01();
+}