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This structure is used to make thousands of calculations in an algorithm like this:

for i:=1 to 900000 do
begin
  CleartheList(MyList);
  DotheMath(MyList);
  DotheChart(MyList);
I am looking for a fast way to initializate the values of my TListSignals to 0 and false.
Now I am using this :
procedure ClearListSignals(var ListSignals:TListSignals);
  i :Integer;
begin
  for i := 0 to MaxSignalRecords - 1 do
  with ListSignals[i] do
  begin
   signal1   :=0;
   signal2   :=0;
   signal3   :=0;
   signal4   :=0;
   signal5   :=0;
   signal6   :=0;
   bsignal1  :=false;
   bsignal2  :=false;
   bsignal3  :=false;
   bsignal4  :=false;
   bsignal5  :=false;
   bsignal6  :=false;
How can I improve the performance of the ClearListSignals procedure?
                So if I was to read the value of any ListSignals[i].signal1 this would equal 0? Nice way to avoid the initial assignments.
– Simon
                Apr 2, 2011 at 7:57
                i suppose answer from ZENsan is more correct. need to use Default and no hack with direct memory access
– Zam
                Dec 1, 2015 at 19:31
                @SolarWind, if the record contains strings have values, ZeroMemory will cause a memory leak. You can call Finalize() on the record first to deallocate the strings before calling ZeroMemory.
– dan-gph
                Jun 27, 2016 at 4:13
                That seems to be the most elegant way. I think that if you have a constructor for a record it should zero the memory for you anyway, so that records work more like classes.
– Mark Patterson
                Nov 28, 2018 at 3:07
                FillChar is defined in System which makes it platform independant, ZeroMemory only works on Windows.
– Jens Mühlenhoff
                Oct 23, 2012 at 11:05
                +1 since it's a good idea. booleans will be aligned on 4 or 8 bytes boundaries, so it's like an awful waste of space, therefore speed in this case.
– Arnaud Bouchez
                Apr 1, 2011 at 6:05
                Really, @A.Bouchez? I thought Booleans were aligned on 1-byte boundaries. Are you saying the total size of the record in the question is 48 instead of 30?
– Rob Kennedy
                Apr 1, 2011 at 6:24
                Booleans will be aligned based on the compiler alignment switch, unless the record is packed. Also, RAM is pretty cheap these days so I would not worry too much about wasted space.
– Misha
                Apr 1, 2011 at 6:40
                @Rob: You're right: use sizeof(TSignalRecord) and you'll get... 32, i.e. there will be 1-byte aligned. And the whole record size is then with packed record, you'll get sizeof(TSignalRecord)=30. With set of 1..6  you'll have sizeof(TSignalRecord)=28.
– Arnaud Bouchez
                Apr 1, 2011 at 6:41
                The issue with wasted space is not the monetary cost of RAM but the speed implications that come with poor use of the cache. But it's not so relevant here because Boolean has an alignment of 1.
– David Heffernan
                Apr 1, 2011 at 8:43
  
The SecureZeroMemory function fills a
  block of memory with zeros. It is
  designed to be a more secure version
  of ZeroMemory.
  
Use this function instead of
  ZeroMemory when you want to ensure
  that your data will be overwritten
  promptly, as the compiler can optimize
  a call to ZeroMemory by removing it
  entirely. 
http://msdn.microsoft.com/en-us/library/aa366877%28v=vs.85%29.aspx
LE: here you have how to use it in Delphi if your version does not contain it:
Using SecureZeroMemory in Delphi
                SecureZeroMemory as its name implies, is a security feature. It's not intended for general purpose use. Optimising compilers only remove the call to ZeroMemory if it detects that the memory is not reused later - implying there's no point in clearing it. However, it's possible that the memory could contain a password, but is not reused later. Then you still want to ensure the password is cleared from memory lest it appear in memory dumps, or be accessible by a hacking attack. In OP's case, there is absolutely no need to use SecureZeroMemory. Though it is useful to be aware of the function.
– Disillusioned
                Apr 2, 2011 at 11:16
        
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