Introduce SbxValues::clear

...to avoid upcoming GCC 8 -Werror=class-memaccess ("clearing an object of non-
trivial type ‘struct SbxValues’")

Change-Id: Icf610e692b81030bfd6f2f940c43ee8bf6f1d4e0
Reviewed-on: https://gerrit.libreoffice.org/48389Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

basic/source/sbx/sbxvalue.cxx

@@ -44,8 +44,7 @@ SbxValue::SbxValue( SbxDataType t ) : SbxBase()
         n = SbxEMPTY;
     else
         SetFlag( SbxFlagBits::Fixed );
-    memset( &aData, 0, sizeof( SbxValues ) );
-    aData.eType = SbxDataType( n );
+    aData.clear(SbxDataType( n ));
 }
 
 SbxValue::SbxValue( const SbxValue& r )
@@ -172,8 +171,7 @@ void SbxValue::Clear()
         default:
         {
             SbxValues aEmpty;
-            memset( &aEmpty, 0, sizeof( SbxValues ) );
-            aEmpty.eType = GetType();
+            aEmpty.clear(GetType());
             Put( aEmpty );
         }
     }
@@ -341,8 +339,7 @@ bool SbxValue::Get( SbxValues& rRes ) const
         {
             // Object contained itself
             SbxDataType eTemp = rRes.eType;
-            memset( &rRes, 0, sizeof( SbxValues ) );
-            rRes.eType = eTemp;
+            rRes.clear(eTemp);
         }
     }
     if( !IsError() )
@@ -753,9 +750,7 @@ bool SbxValue::SetType( SbxDataType t )
                     break;
                 default: break;
             }
-            // This works always, because the Float representations are 0 as well.
-            memset( &aData, 0, sizeof( SbxValues ) );
-            aData.eType = t;
+            aData.clear(t);
         }
     }
     return true;
@@ -1502,9 +1497,8 @@ bool SbxValue::LoadData( SvStream& r, sal_uInt16 )
             case SbxWCHAR:
                 break;
             default:
-                memset (&aData,0,sizeof(aData));
+                aData.clear(SbxNULL);
                 ResetFlag(SbxFlagBits::Fixed);
-                aData.eType = SbxNULL;
                 SAL_WARN( "basic.sbx", "Loaded a non-supported data type" );
 
                 return false;

include/basic/sbxvar.hxx

@@ -24,6 +24,9 @@
 #include <com/sun/star/bridge/oleautomation/Decimal.hpp>
 #include <basic/sbxcore.hxx>
 #include <basic/basicdllapi.h>
+
+#include <cstddef>
+#include <cstring>
 #include <memory>
 
 
@@ -71,6 +74,15 @@ struct SbxValues
     SbxValues(): pData( nullptr ), eType(SbxEMPTY) {}
     SbxValues( SbxDataType e ): eType(e) {}
     SbxValues( double _nDouble ): nDouble( _nDouble ), eType(SbxDOUBLE) {}
+
+    void clear(SbxDataType type) {
+        // A hacky way of zeroing the union value corresponding to the given type (even though the
+        // relevant zero value need not be represented by all-zero bits, in general) without evoking
+        // GCC 8 -Wclass-memaccess, and without having to turn the anonymous union into a non-
+        // anonymous one:
+        std::memset(static_cast<void *>(this), 0, offsetof(SbxValues, eType));
+        eType = type;
+    }
 };
 
 class BASIC_DLLPUBLIC SbxValue : public SbxBase