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, 6 insertions, 1 deletions

diff --git a/include/rapidjson/allocators.h b/include/rapidjson/allocators.h
index 7b348b6b..d3dcb122 100644
--- a/include/rapidjson/allocators.h
+++ b/include/rapidjson/allocators.h
@@ -160,6 +160,9 @@ public:
 

     //! Allocates a memory block. (concept Allocator)

     void* Malloc(size_t size) {

+        if (!size)

+            return NULL;

+

         size = RAPIDJSON_ALIGN(size);

         if (chunkHead_ == 0 || chunkHead_->size + size > chunkHead_->capacity)

             AddChunk(chunk_capacity_ > size ? chunk_capacity_ : size);

@@ -191,7 +194,9 @@ public:
         // Realloc process: allocate and copy memory, do not free original buffer.

         void* newBuffer = Malloc(newSize);

         RAPIDJSON_ASSERT(newBuffer != 0);   // Do not handle out-of-memory explicitly.

-        return std::memcpy(newBuffer, originalPtr, originalSize);

+        if (originalSize)

+            std::memcpy(newBuffer, originalPtr, originalSize);

+        return newBuffer;

     }

 

     //! Frees a memory block (concept Allocator)