Problem to copy objects

ROOT
#1

Dear Rooters

The attached macro “macroTestCopy.C” shows my problems:

1, Why do methods CopyProjectInfo2() and CopyProjectInfo3() not work?
“.x macroTestCopy.C+” does not print ProjectC and ProjectD, while
“.x macroTestCopy.C” crashes.

2, Why does function TestCopy1() not work?

3, In my real program I need to copy objects, which are created on
the heap (as shown in function TestCopy1()):
What do I need to do to copy an object created on the heap?

Thank you in advance for your help.
Best regards
Christian
macroTestCopy.C (8.64 KB)

#2

Hi Christian,

Your program will work if you fix a bug in your code in
MyClass::CopyProjectInfo3
You are adding to a TList a local object XprojectInfo that is destroyed
when leaving the function. As a result you have a pointer to a dead object
in the TList

Rene

#3

Dear Rene

Thank you, I understand the error, but I have no idea how to solve it.
When I try to create “infocopy” on the heap I get an error.

Furthermore, my real problem is that I would like to use function
"TestCopy1()" which I have commented out since it will not compile.

Best regards
Christian

#4

Hi Christian,

Well! your function TestCopy1 has also several C++ errors.
Change it to:

[code]void TestCopy1()
{
// Test copying of class XProjectInfo

MyClass *myclass = new MyClass(“MyClass”,“test”);

myclass->ProjectInfo(“ProjectA”, 22052005, “descriptionA”);

XProjectInfo *infoB = new XProjectInfo(“ProjectB”, 22052005, “descriptionB”);

myclass->CopyProjectInfo1(*infoB);

XProjectInfo *infoC = new XProjectInfo(“ProjectC”, 22052005, “descriptionC”);

myclass->CopyProjectInfo2(*infoC);

XProjectInfo *infoD = new XProjectInfo(“ProjectD”, 22052005, “descriptionD”);

myclass->CopyProjectInfo3(infoD);

myclass->PrintData(“ProjectA”);
myclass->PrintData(“ProjectC”);
myclass->PrintData(“ProjectB”);
myclass->PrintData(“ProjectB”);

delete myclass;
delete infoB;
delete infoC;
delete infoD;
}[/code]

Rene

#5

Hi Christian,

Why do you have

XProjectInfo *infocopy = new XProjectInfo(); infocopy->Copy(info); fList->Add(infocopy);
but you also have

// XProjectInfo *infocopy = new XProjectInfo(); XProjectInfo infocopy; info->Copy(infocopy); fList->Add(&infocopy);
I think that the second should be

XProjectInfo *infocopy = new XProjectInfo(); infocopy->Copy(info); fList->Add(&infocopy); I.e. fix both the memory error and the copy direction error.
Also this can not work in interpreted mode since you class derived from a compiled class AND overload a virtual function.

Cheers,
Philippe.

#6

Dear Rene, dear Philippe

Thank you, I did not know that I can write Function(*var), i.e.
myclass->CopyProjectInfo1(*infoB);

The code of CopyProjectInfo3(XProjectInfo *info) must be:

   XProjectInfo *infocopy = new XProjectInfo();
   info->Copy(*infocopy);
   fList->Add(infocopy);

Additionally, I could also use:

   XProjectInfo *infocopy = (XProjectInfo*)info->Clone();
   fList->Add(infocopy);

Are there any rules, when to use obj->Copy() and when to use obj->Clone()?
Which one should normally be used?

BTW, now my macro works also in interpreted mode :slight_smile:

Best regards
Christian