I am looking at something that I discovered in an old code base, and I am pretty confused.
Here is a function definition:
void vUpdateSequenceDetailsAndIncrement(
const CallEvent& roCPEvent,
const CallInfo& roCallInfo,
BOOL bCreationEvent);
Here it is being called:
vUpdateSequenceDetailsAndIncrement(roCPEvent, NULL, FALSE);
Here NULL is being passed directly to the reference parameter roCallInfo
. This function eventually calls:
vTimeChange(*pSeqDetails, roCPEvent, roCallInfo);
which is defined:
void vTimeChange(const SequenceDetails& roSequenceDetails,
const CallEvent& roCPEvent,
const CallInfo& roCallInfo)
Again passing the possibly NULL value to roCallInfo
. I thought that NULL could not be passed as a reference? Does anyone know if VC++ 4.x had some kind of problem which made this kind of code okay? If NULL can be passed as a reference then what happens when in vTimeChange something like this happens:
roCallInfo.getCallStartTime();
Is that not a dereference of NULL in the same way as if I were to do
CallInfo * info = NULL;
info->getCallStartTime();
? I'll probably put a guard in there anyways and let the compiler remove it if unnecessary, but I'd love to get to the bottom of how this is happening!
Thanks.
Depends on how NULL is defined in VC 4.2
If it is just
#define NULL 0
then you are actually getting this under the hood:
vUpdateSequenceDetailsAndIncrement(roCPEvent, CallInfo(0), FALSE);
and reference of temp var of type CallInfo is passed to the function (if CallInfo has compatible ctor)