Zeroing Memory at Allocation

The memory allocated by malloc or similar C-Runtime functions is not initialized to zero according to the C99 specification, which Windows follows. To maintain backwards compatibility, RTX64 provides a Zero memory on allocation setting in the Control Panel.

For backwards compatibility, this setting is enabled by default. When this setting is disabled, memory requests from some C-Runtime functions or RTAPIs will not be initialized to zero at allocation. However, by definition, memory requests from calloc/_recalloc, VirtualAlloc, and HeapAlloc/HeapReAlloc with the HEAP_ZERO_MEMORY flag will be initialized to zero at allocation.

NOTE: In RTX64 3.x and earlier, RTX64 always zeroed memory.

NOTE: To improve performance, you should disable this setting once you are sure your processes do not depend on zero memory.

The table below lists the initialization status of the returning memory from various C-Runtime functions and RTAPIs:

Functions	Zero Memory At Allocation disabled	Zero Memory At Allocation enabled
malloc/new/realloc/_expand	Not zeroed	Zeroed (RTSSRelease configuration only)
calloc/_recalloc	Zeroed	Zeroed
RtAllocateLocalMemory	Not zeroed	Zeroed
RtAllocateLocalMemoryEx without RTALLOC_NOT_ZERO_MEMORY flag	Not zeroed	Zeroed
RtAllocateLocalMemoryEx with RTALLOC_NOT_ZERO_MEMORY flag	Not zeroed	Not zeroed
HeapAlloc/HeapReAlloc without HEAP_ZERO_MEMORY	Not zeroed	Zeroed
HeapAlloc/HeapReAlloc with HEAP_ZERO_MEMORY	Zeroed	Zeroed
VirtualAlloc	Zeroed	Zeroed
RtAllocateLockedMmeory	Not zeroed	Zeroed
RtCreateSharedMemory	Not zeroed	Zeroed

NOTE: The behavior of initializing memory to zero at allocation is the same whether you use local memory or Windows memory.