Re: std::vector: Memory allocation in copy constructor for empty vector

[Paolo Carlini <pcarlini at suse dot de>]

... the below is the variant which I tested on x86 and x86_64 and I mean 
to actually commit. Note that leaving out any additional check in 
deallocate is actually much better from the point of view of binary 
compatibility between objects built with patched/unpatched headers: with 
this version should be perfectly safe to pass vectors between such two 
objects.

Paolo.

///////////////////
2007-09-06  Paolo Carlini  <pcarlini@suse.de>

	* include/bits/stl_vector.h (_Vector_base<>::_M_allocate):
	Do not call _M_impl.allocate when __n == 0.
	* testsuite/23_containers/vector/zero_sized_allocations.cc: New.

Index: include/bits/stl_vector.h
===================================================================
--- include/bits/stl_vector.h	(revision 128180)
+++ include/bits/stl_vector.h	(working copy)
@@ -125,7 +125,7 @@
 
       _Tp*
       _M_allocate(size_t __n)
-      { return _M_impl.allocate(__n); }
+      { return __n != 0 ? _M_impl.allocate(__n) : 0; }
 
       void
       _M_deallocate(_Tp* __p, size_t __n)
Index: testsuite/23_containers/vector/zero_sized_allocations.cc
===================================================================
--- testsuite/23_containers/vector/zero_sized_allocations.cc	(revision 0)
+++ testsuite/23_containers/vector/zero_sized_allocations.cc	(revision 0)
@@ -0,0 +1,77 @@
+// Copyright (C) 2007 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, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
+// USA.
+//
+// As a special exception, you may use this file as part of a free software
+// library without restriction.  Specifically, if other files instantiate
+// templates or use macros or inline functions from this file, or you compile
+// this file and link it with other files to produce an executable, this
+// file does not by itself cause the resulting executable to be covered by
+// the GNU General Public License.  This exception does not however
+// invalidate any other reasons why the executable file might be covered by
+// the GNU General Public License.
+
+#include <vector>
+#include <cstdlib>
+#include <testsuite_hooks.h>
+
+unsigned int zero_sized_news = 0;
+
+void *operator new(size_t size) throw (std::bad_alloc)
+{
+  /* malloc(0) is unpredictable; avoid it.  */
+  if (size == 0)
+    {
+      size = 1;
+      ++zero_sized_news;
+    }
+
+  void *p = std::malloc(size);
+
+  if (p == 0)
+    throw std::bad_alloc();
+
+  return p;
+}
+
+void operator delete(void *ptr) throw()
+{
+  if (ptr != 0)
+    std::free(ptr);
+}
+
+// http://gcc.gnu.org/ml/libstdc++/2007-09/msg00006.html
+void test01()
+{
+  bool test __attribute__((unused)) = true;
+
+  std::vector<std::vector<int> > *v;
+  VERIFY( zero_sized_news == 0 );
+
+  v = new std::vector<std::vector<int> >;
+  VERIFY( zero_sized_news == 0 );
+
+  v->resize(10);
+  delete(v);
+  VERIFY( zero_sized_news == 0 );
+}
+
+int main()
+{
+  test01();
+  return 0;
+}