Hi,

this fixes the PR by checking for zero in check_default_argument and, in case, replacing it with nullptr to avoid further warnings later on. Should be safe enough for 4.7.1 too.


Tested x86_64-linux.

Thanks,
Paolo.

/////////////////////
/cp
2012-03-29  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/52718
        * decl.c (check_default_argument): With -Wzero-as-null-pointer-constant
        warn for a zero as null pointer constant default argument.

/testsuite
2012-03-29  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/52718
        * g++.dg/warn/Wzero-as-null-pointer-constant-5.C: New.




Index: testsuite/g++.dg/warn/Wzero-as-null-pointer-constant-5.C
===================================================================
--- testsuite/g++.dg/warn/Wzero-as-null-pointer-constant-5.C    (revision 0)
+++ testsuite/g++.dg/warn/Wzero-as-null-pointer-constant-5.C    (revision 0)
@@ -0,0 +1,20 @@
+// PR c++/52718
+// { dg-options "-Wzero-as-null-pointer-constant" }
+
+struct foo
+{
+  foo(void* a = 0) {};      // { dg-warning "zero as null pointer" }
+};
+
+void* fun(void* a = 0) {};  // { dg-warning "zero as null pointer" }
+
+struct bar: foo
+{
+  bar() {};
+};
+
+struct baz
+{
+  baz(const foo& f1 = foo(),
+      void* f2 = fun()) {};
+};
Index: cp/decl.c
===================================================================
--- cp/decl.c   (revision 185969)
+++ cp/decl.c   (working copy)
@@ -10596,6 +10602,17 @@ check_default_argument (tree decl, tree arg)
       return error_mark_node;
     }
 
+  if (warn_zero_as_null_pointer_constant
+      && c_inhibit_evaluation_warnings == 0
+      && (POINTER_TYPE_P (decl_type) || TYPE_PTR_TO_MEMBER_P (decl_type))
+      && null_ptr_cst_p (arg)
+      && !NULLPTR_TYPE_P (TREE_TYPE (arg)))
+    {
+      warning (OPT_Wzero_as_null_pointer_constant,
+              "zero as null pointer constant");
+      return nullptr_node;
+    }
+
   /* [dcl.fct.default]
 
      Local variables shall not be used in default argument

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