TClass::GetClass("MyClassName)->New() Fails

ROOT
1

Please read tips for efficient and successful posting and posting code

Please fill also the fields below. Note that root -b -q will tell you this info, and starting from 6.28/06 upwards, you can call .forum bug from the ROOT prompt to pre-populate a topic.

ROOT Version: 6.36.02
Platform: macosx64
Compiler: Not Provided

Hello…

I have used the following code for a while:

TClass *taskClass = TClass::GetClass(taskClassName);
**if** (!taskClass)
   **throw** Exception();
Task * task = **static_cast**<Task*>(taskClass->New());

This usually works great! It enables me to create jobs based on a workflow file… But today I added a new class that inherits from my class Task. And I get the following message

Error in <TClass::New>: cannot create object of class CAP::ThermalModelTask
*** Break *** segmentation violation
\[/usr/lib/system/libsystem_platform.dylib\] \_sigtramp (no debug info)
\[/usr/local/Cellar/root/6.36.02/lib/root/libCling.so\] cling::TransactionPool::releaseTransaction(cling::Transaction\*, bool) (no debug info)\[/Users/aa7526/Documents/GitHub/CAP8.0/build/CAP\] main (no debug info)
\[/usr/lib/dyld\] start (no debug info)

The new class has a default constructor (with no argument), a copy constructor, as well as a virtual DTOR. It is defined in my own namespace CAP. The only difference is that this new class is a different folder and library built with cmake. But my other classes are all built that way. Is there a way to have a more verbose output that might identify why the instantiation fails?

As always, thanks in advance!!

Claude

2

There is no embedded extra output but you can add the following diagnosis code:

TClass *taskClass = TClass::GetClass(taskClassName);
if (!taskClass)
   throw Exception();
if (!taskClass->IsLoaded())
    std::cerr << "Debug: the TClass for " << taskClass->GetName() << " is not marked as loaded.  It's state is: << taskClass->GetState() << '\n';
if (!taskClass->GetNew())
    std::cerr << "Debug: the TClass for " << taskClass->GetName() << " does not have the accelerator function/wrapper for the constructor\n";
Task * task = **static_cast**<Task*>(taskClass->New());
3

Hi Philip

Thanks for the suggestion. I tried it and the accelerator function/wrapper is not available. Yet, I am defining that class like the others. Any thoughts?

Thanks again.

4

Is the TClass marked as loaded or not?

5

Yes. The class is marked as loaded. But the “new” operator is not available.

6

Ok. So somehow, rootcling thinks that the class can not be instantiated, common cause are:

  • the class is abstract (one of the abstract virtual function is not overloaded/implemented).
  • the default constructor is not public

Do you have a link to the header file for that class?

7

Brilliant! The “public:” keyword was missing. Thank you so very much!!!

Claude