Thread: Unique pointer and a vector in the class constructor

  1. #1
    Registered User
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    May 2008
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    Unique pointer and a vector in the class constructor

    Hello,

    I was mildly surprised when I realized that I cannot initialize the vector directly like in the commented out command, but have to use a default constructor. Surprised because initialization directly via the constructor (i.e. without a unique pointer) works fine. I am doing this right, or is there a better way? Because doing it this way on a class with many vectors bloats the code.

    Code:
    #include <iostream>
    #include <memory>
    #include <vector>
    
    struct Gauge
    {
        std::vector<int> Dial;
        Gauge() = default;
        Gauge(std::vector<int> dial) : Dial(dial) {}
    };
    
    int main ()
    {
        // auto gauge = std::make_unique<Gauge> ({1,2});
        auto gauge = std::make_unique<Gauge> ();
        gauge->Dial = {1,2};
        std::cout << gauge->Dial[0] << '\n';
    }

  2. #2
    C++ Witch laserlight's Avatar
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    I think you may need a std::initializer_list constructor to do that. If you don't go that route, what about:
    Code:
    auto gauge = std::make_unique<Gauge>(std::vector{1, 2});
    But an initializer_list constructor might be better so as to not expose the internals of the class... but you already have the member variable as public so it might not matter.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
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    May 2008
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    Yes, this works! Thank you!

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