How to customize seconds with SetTimeFormat?

ROOT
1

Hello,

I am playing with SetTimeFormat and I am facing same issue as Configure sub-second display for a time axis.

I noticed that seconds are formatted as XsYYY. I want to customize, how to fix that ?
I would expect that %S should just return a number. The following format “%Y-%m-%d %H:%M:%S %Z” should return “2024-09-19 22:16:22 JST” not “2024-09-19 22:16:22s JST”

Alternatively is it possible to pass a function either to SetTimeFormat of SetLabelFormat ?
I am considering to use my how implementation SetLabelFormat("MyMethod(%s)")

Thank you
M.

2

Hello Marco,

I am sure @couet and @linev have ideas about how to proceed.

Best,
D

3

There is no SetLabelFormat for the TAxis.
And SetTimeFormat supports only arguments listed here:

https://root.cern/doc/master/classTGaxis.html#GA14

It is not possible to invoke any function when formatting time axis labels.

4

Thank you linev for your confirmation.

From documentation there is an issue the time format. After looking at the code, it seems that TGAxis::SetTimeOffset is doing some fancy modifications of the time format. I believe this method should actually just store the offset information for computing the final result in the final method TGaxis::PaintAxis

%S is maybe not made to handle microtime in the first place, but one nice input would be to introduce %.2S such that we can control decimals (that is not the case at the moment, I believe)

void TGaxis::SetTimeOffset(Double_t toffset, Option_t *option)
{
   TString opt = option;
   opt.ToLower();

   char tmp[20];
   time_t timeoff;
   struct tm* utctis;
   
   Int_t idF = fTimeFormat.Index("%F");
   if (idF>=0) fTimeFormat.Remove(idF);
   fTimeFormat.Append("%F");

   timeoff = (time_t)((Long_t)(toffset));

   // offset is always saved in GMT to allow file transport
   // to different time zones
   utctis = gmtime(&timeoff);

   if (utctis != nullptr) {
      strftime(tmp, 20,"%Y-%m-%d %H:%M:%S",utctis);
      fTimeFormat.Append(tmp);
   } else {
      fTimeFormat.Append("1970-01-01 00:00:00");
   }

   // append the decimal part of the time offset
   Double_t ds = toffset-(Int_t)toffset;
   snprintf(tmp,20,"s%g",ds);
   fTimeFormat.Append(tmp);

   // add GMT/local option
   if (opt.Contains("gmt")) fTimeFormat.Append(" GMT");
}

Additionally, I don’t understand the purpose of the option parameter.
As an international standard, this should be written as UTC I believe.

5

Reading source code - I see usage strftime function which does not support fractional part of the seconds. ROOT manually adds fraction if %S appears in format string - but it always 5 digits after the “.”. See:

Maybe one can add some static variable at this place.
I guess @couet can have better idea

6

Yes microtime are not handle. The resolution is the second.

7

Ok, then I think I will not use SetTime* options. Thank you for the support.
I will most like set the first bin to 0 and based on the number of bins recompute the time axis on my own.

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8

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