CODEWITHSUNDEEP
c++structinitializer-listvalarray
pmakal
pmakal

Reputation: 79

Initializing struct via member initialization list

So I'm learning C++ from Stephen Prata book and I want to do one exercise... So the problem is this:

I want to use a std::valarray inside a struct, inside a class like this:

class Wine
{
private:
    struct Pair
    {
        std::valarray<int> valYear;
        std::valarray<int> valBottlesNum;
    };
    int m_yearNum;
    Pair m_numericData;
public:
    Wine();
    Wine(int, const int[], const int[]);
};

And initialize this via member initialization list:

Wine::Wine(int yearNum, const int year[], const int bottlesNum[])
    : m_yearNum(yearNum), 
    m_numericData.valYear(yearNum, year), 
    m_numericData.valBottlesNum(yearNum, bottlesNum)
{}

But it just doesn't want to work. Somehow compiler does not like this "." to access members of a m_numericData struct in a initializer list.

I could just abandon Pair struct and do valYear and valBottlesNum as a simple class member variables and initilize them like this...

Wine::Wine(, int yearNum, const int year[], const int bottlesNum[])
    : m_yearNum(yearNum), m_valYear(yearNum, year), m_valBottlesNum(yearNum, bottlesNum)
{}

but I really want to know how to solve this kinda stuff.

Thanks in adavnce!

Upvotes: 2

Views: 3233

Answers (2)

Praetorian
Praetorian

Reputation: 109149

The valarray constructor you're attempting to use takes a T const* to the data and an std::size_t argument indicating the number of array elements that the first argument points to. If you can use C++11, then change yearNum to std::size_t and you can use list-initialization, which in turn will aggregate initialize the Pair.

Wine::Wine(std::size_t yearNum, const int year[], const int bottlesNum[])
    : m_yearNum(yearNum)
    , m_numericData{{year, yearNum}, {bottlesNum, yearNum}}
{}

Live demo

Upvotes: 2

Jonathan Potter
Jonathan Potter

Reputation: 37132

You can move the individual initialisations into the body of the constructor:

Wine::Wine(int yearNum, const int year[], const int bottlesNum[])
    : m_yearNum(yearNum)
{
    m_numericData.valYear = std::valarray<int>(yearNum, year);
    m_numericData.valBottlesNum = std::valarray<int>(yearNum, bottlesNum);
}

Alternatively, give Pair its own constructor.

Upvotes: 2

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