How can i return unique_ptr with pointer function?

Question

i don't understand fully this problem. This is my function and i need return class with unique_ptr how can i this?

my list:

std::list<std::unique_ptr<Maths> > l_MathsList;

my function

Maths* Maths2::FindMathsID(int iID)
{
    auto mpClass= std::unique_ptr<Maths>();
    for (auto&& it : l_MathsList)
    {
        if (iter->IsMy(iID)) { 
            mpClass = std::move(it); 
            }
            break; 
        }
    }
    return mpClass; // compiler error

You've declared a function which returns a Maths* and then you've elected to return a std::unique_ptr. The compile error likely tells you as much. Either change the return type or quit making a smart pointer. — Silvio Mayolo
– Silvio Mayolo, Commented Jul 2, 2021 at 21:58
@SilvioMayolo thanks for your comment! Can u give example for return type? Compiler error: cannot convert 'std::unique_ptr<MathFuncs::Maths>' to 'MathFuncs::MathFuncs*' in return — CILGINIMAM
– CILGINIMAM, Commented Jul 2, 2021 at 21:59
If you intend to return a unique_ptr, then the return type should be std::unique_ptr<Maths>. But note that, once you've called this function once, some prefix of the list l_MathsList (which I presume is an instance variable) will be left empty and therefore inaccessible. — Silvio Mayolo
– Silvio Mayolo, Commented Jul 2, 2021 at 22:01
@SilvioMayolo i need this but i wish using smart ptr working func: ` Maths * mClass= NULL; for (auto it = l_MathsList.cbegin(); it != l_MathsList.cend(); it++) { if ((*it)->IsMy(iID)) { mClass= *iter; if ( (parameter2)!= NULL) { mClass->ReCalc(parameter2); } break; } } return mClass; ` — CILGINIMAM
– CILGINIMAM, Commented Jul 2, 2021 at 22:03
If the requirement is to "return a ...", then declare your function to so just that. Work on figuring out how to accomplice the task and ... question the task. — Ted Lyngmo
– Ted Lyngmo, Commented Jul 2, 2021 at 22:07

Hatted Rooster · Accepted Answer · 2021-07-02 22:14:36Z

1

You probably just want to return a non-owning pointer to the collection element right?

In that case just use .get():

Maths* Maths2::FindMathsID(int iID)
{
    for (auto& it : l_MathsList)
    {
        if (it->IsMy(iID))
          return it.get();
    }
    return nullptr;
}

answered Jul 2, 2021 at 22:14

Hatted Rooster

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