Define and instantiate C style array of string inside class

I am trying to create a class with an array of string defined inside. I want this array of string to be defined when the class is instantiated.

Here is my attempt below (or the code showing my intentions).

class a_class
{
  public:
    static char const *arr_str[];
    int idx;
    void a_function();
  private:
};

a_class MyClass({"aaa", "bbb", "ccc"}, 3);

Obviously the above code does not compile well at all.

How can I achieve this?

Your array is static, so it is not tied to any specific instance of a_class. You should not be using an instance constructor to initialize it. In modern C++, you can initialize a static class member right in its declaration.

Also, your class does not explicitly define a non-default constructor (ie a constructor that requires arguments be passed in), as such you can't use parenthesis when constructing a new instance of the class while passing in argument values, as your example is doing. The compile will fail with an error about a matching constructor not being found. So, you will have to use curly-braces instead to initialize the non-static member directly.

Try this:

class a_class
{
  public:
    static constexpr char const *arr_str[] = {"aaa", "bbb", "ccc"};
    int idx;
    void a_function();
  private:
};

a_class MyClass{3};

Live Demo

On the other hand, if you want a per-instance array, then it should not be a static member, eg:

template<size_t N>
class a_class
{
  public:
    char const* arr_str[N];
    int idx;
    void a_function();
  private:
};

template<size_t N>
a_class(char const * (&&)[N], int) -> a_class<N>;

a_class MyClass{{"aaa", "bbb", "ccc"}, 3};

Live Demo

Alternatively, use a dynamic-sized std::vector instead of a fixed-sized array, eg:

#include <vector>

class a_class
{
  public:
    std::vector<char const*> arr_str;
    int idx;
    void a_function();
  private:
};

a_class MyClass{{"aaa", "bbb", "ccc"}, 3};

Live Demo