C++ std::unique_ptr return from function and test for null

Either of the following should work:

return std::unique_ptr<myClass>{};
return std::unique_ptr<myClass>(nullptr);

To test whether the returned object points to a valid object or not, simply use:

if ( returnedData )
{
   // ...
}

See http://en.cppreference.com/w/cpp/memory/unique_ptr/operator_bool.

Yes it's possible. A default constructed unique_ptr is what you want:

Constructs a std::unique_ptr that owns nothing.

// No data found
return std::unique_ptr<myClass>{};

That is equivalent to the nullptr_t constructor, so perhaps this is more clear:

// No data found
return nullptr;

Yes, it is possible. A default constructed unique_ptr or one constructed from nullptr can be considered null:

std::unique_ptr<MyClass> getData()
{
    if (dataExists)
        return std::make_unique<MyClass>();
    return nullptr;
}

To test for null either compare against nullptr or take advantage of conversion to bool:

int main()
{
    std::unique_ptr<MyClass> returnedData = getData();

    if (returnedData)
    {
        ... 
    }
}

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