TRandom3::SetSeed(), strange behavior

ROOT
1

Dear Root-Experts,

(Root 5.22/00)

I would like to report a behavior of TRandom3::SetSeed(UInt_t seed = 0) in interpreted mode, which I didn’t expect. I am not sure if this is a bug or a feature.

The following macro demonstrates the problem:

#include <TRandom3.h> #include <iostream> void RandomTest(){ // TRandom3 * randomGen = new TRandom3(0); // randomGen->SetSeed(0); cout<<" seed1: "<< randomGen->GetSeed()<<endl; // randomGen->SetSeed(); cout<<" seed2: "<< randomGen->GetSeed()<<endl; // }

The expected output looks like this:

root RandomTest.C++ root [0] Processing RandomTest.C++... Info in <TUnixSystem::ACLiC>: creating shared library /misc/home/he/aadametz/./RandomTest_C.so seed1: 1249051090 seed2: 1249051090

But when the macro is run in interpreted mode

~> root RandomTest.C root [0] Processing RandomTest.C... seed1: 1249051092 seed2: 65539

seed2 is 65539, which is the default value in TRandom::SetSeed(UInt_t seed = 65539).

So somehow the SetSeed method of TRandom is picked up, instead of the TRandom3-version, when SetSeed() is used without explicitly specified argument.

Best regards,
Aleks

2

Hi Aleks,

This is an unfortunate (but unavoidable) consequence of a space optimization in the CINT dictionary. The CINT dictionary do not explicitly record the overload in derived class … and thus do not record changes in the default values either (if the base overload and the derived overload have different default value like TRandom and TRandom3).

Cheers,
Philippe.

3

Hi Philippe,

thank you for the quick answer. I didn’t know about that limitation of CINT.

Regards,
Aleks