vo001_AdoptOrOwnMemory¶

In this tutorial we learn how the RVec class can be used to adopt existing memory or allocate some.

Author: Danilo Piparo
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Tuesday, March 28, 2023 at 10:03 AM.

In [1]:

import ROOT

Welcome to JupyROOT 6.29/01

We use this class for didactic purposes: upon copy, a line is printed to the terminal.

In [2]:

ROOT.gInterpreter.Declare('''
class UponCopyPrinter {
public:
   UponCopyPrinter() = default;
   UponCopyPrinter(UponCopyPrinter &&) = default;
   UponCopyPrinter(const UponCopyPrinter &) { std::cout << "Invoking copy c'tor!" << std::endl; }
};
''')

RVec_UponCopyPrinter = ROOT.ROOT.VecOps.RVec(ROOT.UponCopyPrinter)

One of the essential features of RVec is its ability of adopting and owning memory.

Let's create an RVec of UponCopyPrinter instances. We expect no printout:

In [3]:

v = RVec_UponCopyPrinter(3)

Let's adopt the memory from v into v2. We expect no printout:

In [4]:

v2 = RVec_UponCopyPrinter(v.data(), v.size())

OK, let's check the addresses of the memory associated to the two RVecs It is the same!

In [5]:

print("%s and %s" %(v.data(), v2.data()))

<cppyy.gbl.UponCopyPrinter object at 0xd6db1b0> and <cppyy.gbl.UponCopyPrinter object at 0xd6db1b0>

Now, upon reallocation, the RVec stops adopting the memory and starts owning it. And yes, a copy is triggered. Indeed internally the storage of the RVec is an std::vector. Moreover, the interface of the RVec is very, very similar to the one of std::vector: you have already noticed it when the data() method was invoked, right?

In [6]:

v2.resize(4)

Of course, now the addresses are different.

In [7]:

print("%s and %s" %(v.data(), v2.data()))

<cppyy.gbl.UponCopyPrinter object at 0xd6db1b0> and <cppyy.gbl.UponCopyPrinter object at 0xd731420>