Can I use `TFile::Write()` to write a temporary object?

ROOT
1

Dear experts

I have a “handle” class IHandle derived from TObject, and that class is a kind of shared_ptr with -> operator overloaded, and the pointer pointing to pointee is inside IHandle.

Now I have another function GetHandle(), that returns the IHandle of some object, let’s say IHandle<CLASSA>. I try to save it into TFile by using:

GetHandle()->Write();

will this cause crash or memory issue like dangling pointer? the Object of IHandle will only valid until the end of this line I suppose.

2

Hi @Crisps , thanks for your report!
@pcanal do you think you can help with this?

3

Related: Is shared_ptr supported in class member derived from TObject? - #5 by pcanal

4

with -> operator overloaded, and the pointer pointing to pointee is inside IHandle.
GetHandle()->Write();

I am not sure from your description what object is temporary. operator-> is putting on the stack (per se) (and/or using a temporary for) the value of the pointer to the pointee (so the pointee, the object is not temporary).

Either way calling TObject::Write on a temporary is in general just fine since by C++ rule that temporary lifetime will extent to the end of the statement.

5

Sorry for the unclear description.
IHandle is a class contains a pointer value pointing to some object, and also a count number (just like shared_ptr)
You mean as long as the object is valid before the end of the statement (“;” sign) it can be successfully written?
If it’s a IHandle class with -> overloaded, and called handleToClassA->Write() where handleToClassA is the type of IHandle<ClassA>, will the IHandle object itself (with the pointer value 0xADDRESS) been written in TFile or will the pointee ClassA been written?

6

Indeed.

7

By definition, in that scenario, Write never sees the handle since it is called on the pointee’s address (that’s the ‘magic’ of the operator-> overload.
I.e. the pointee ClassA will be written?