In Java, there are 2 ways: A. use messages to trigger that object into doing your bidding. B. static keyword. Plan B needless to say is not so "safe". I wonder how things are done in C++？ I want to do something that is a tad bit on the complicated side and yet the code was already done I just need to call it - but it's in another compilation unit so technically I'm not supposed to call it from "here". Someone please enlighten me? Quick recap: Object A want to do thing X. Object B already has a function that does precisely thing X. I want to execute that function from within A, which I shouldn't, what's the best workaround?

Hi, easiest is just to create an instance of Object B somewhere inside one of your Object A's functions and then call Object B's function using that instance of Object B, say something like: #include "ObjectA.h" #include "ObjectB.h" void ObjectA::functionA() { ... ObjectB b; b.functionB(); ... } If the 2 objects are within the same compilation unit or not doesn't matter. P.S. That particular instance of ObjectB is shortlived and dies when functionA() exits, so if you want to remember some value or state from Object B you have to store it somewhere in Object A.

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How do I safely call methods from another object?

Unsolved C++ Gurus

21 Posts 4 Posters 5.3k Views

J J.Hilk

@jsulm possible, we simply don't know enough of the actual code to say for sure.

However, am I wrong here, or is "xxxx not decleared in the scope error " not usually a sign of missing includes ?
I tried to use connect on a null pointer recently.
It compiled, it run, it did not crash, I only got a warning " cannot connect to nullptr".

More infos needed!
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J Offline
jsulm
Lifetime Qt Champion
wrote on last edited by

#21
@J.Hilk
```
connect((QObject*)sender, SIGNAL(newNodeAdded()), this, SLOT(onRefreshnodeClicked()));
```
"sender not decleared in the scope"
https://forum.qt.io/topic/113070/qt-code-of-conduct
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