"Avoid unnamed objects ..." warning when using QDomNode::appendChild

Bart_Vandewoestyne

Using Qt 5.12.4, quite recently we switched from Visual Studio 2015 to Visual Studio 2019. Using Visual Studio 2019, the lines

QDomDocument doc;
const auto fooElement = doc.createElement("Foo");
doc.appendChild(fooElement);

result in the warning

C26444 Avoid unnamed objects with custom construction and destruction (es.84).

Looking at the documentation at https://doc.qt.io/qt-5/qdomnode.html#appendChild I see that appendChild returns a new reference to fooElement on success or a null node on failure. Does that mean I could do something like the following to make the warning go away?

QDomDocument doc;
auto fooElement = doc.createElement("Foo");
fooElement = doc.appendChild(fooElement).toElement();
if (fooElement.isNull()) {
    // handle error case
}
// do stuff with fooElement

or am I misunderstanding things here?

jsulm

@Bart_Vandewoestyne said in "Avoid unnamed objects ..." warning when using QDomNode::appendChild:

Does that mean I could do something like the following to make the warning go away?

Did you try?

https://docs.microsoft.com/en-us/visualstudio/code-quality/c26444?view=vs-2019

Bart_Vandewoestyne

Yes, I did, and the warning goes away. I was just wondering if

doc.appendChild(fooElement)
// do stuff with fooElement

was going to do the same as

fooElement = doc.appendChild(fooElement).toElement();
// do stuff with fooElement

Using VS2019, I checked the value of fooElement's impl pointer, and the value before and after the call to

fooElement = doc.appendChild(fooElement).toElement();

was the same. So to be really on the safe side, I would say that

QDomDocument doc;
auto fooElement = doc.createElement("Foo");
fooElement = doc.appendChild(fooElement).toElement();
if (fooElement.isNull())
{
    // handle error
}
// do stuff with fooElement

is the safest way to append the child. However, I often simply see

QDomDocument doc;
const auto fooElement = doc.createElement("Foo");
doc.appendChild(fooElement);

from which I would think that most often, people simply do not check for appendChild errors.

Any comments on this? Am I overlooking something? Could C++17's [[maybe_unused]] attribute come in handy here? Feel free to share thoughts.