Avoid calling memcpy with NULL pointers

According to the C/C++ standards, calling `memcpy(NULL, NULL, 0)` is
undefined behaviour. Recent GCC versions may rely on this by optimizing
NULL pointer checks more aggressively, see [1].

This patch tries to avoid calling std::memcpy with zero elements.
As a side effect, explicitly return NULL when requesting an empty block
from MemoryPoolAllocator::Malloc.

This may be related to #301.

[1] https://gcc.gnu.org/gcc-4.9/porting_to.html

1 files changed, 12 insertions, 4 deletions

diff --git a/include/rapidjson/document.h b/include/rapidjson/document.h
index 204e3bde..3aaef13b 100644
--- a/include/rapidjson/document.h
+++ b/include/rapidjson/document.h
@@ -1582,16 +1582,24 @@ private:
     // Initialize this value as array with initial data, without calling destructor.

     void SetArrayRaw(GenericValue* values, SizeType count, Allocator& allocator) {

         flags_ = kArrayFlag;

-        data_.a.elements = (GenericValue*)allocator.Malloc(count * sizeof(GenericValue));

-        std::memcpy(data_.a.elements, values, count * sizeof(GenericValue));

+        if (count) {

+            data_.a.elements = (GenericValue*)allocator.Malloc(count * sizeof(GenericValue));

+            std::memcpy(data_.a.elements, values, count * sizeof(GenericValue));

+        }

+        else

+            data_.a.elements = NULL;

         data_.a.size = data_.a.capacity = count;

     }

 

     //! Initialize this value as object with initial data, without calling destructor.

     void SetObjectRaw(Member* members, SizeType count, Allocator& allocator) {

         flags_ = kObjectFlag;

-        data_.o.members = (Member*)allocator.Malloc(count * sizeof(Member));

-        std::memcpy(data_.o.members, members, count * sizeof(Member));

+        if (count) {

+            data_.o.members = (Member*)allocator.Malloc(count * sizeof(Member));

+            std::memcpy(data_.o.members, members, count * sizeof(Member));

+        }

+        else

+            data_.o.members = NULL;

         data_.o.size = data_.o.capacity = count;

     }