Initialization of const array in C++

Question

I need to initialize a const int array in a class constructor via initialization list in C++.

I know that there is an easy solution of this problem based on using extended initialization list.
Still, I want to avoid using -std=c++11 or -std=gnu++11.
Obviously, I know from the beginning that its size is 4 and the content is {1, 2, 3, 4}.

Because a char is simply a byte, it can hold values in the range 0 to 255 or -128 to 127, depending on whether it is signed or not. — Jack Aidley, Apr 07 '13 at 12:01
Why do you _need_ to initialize a `const int` array in a class constructor via initialization list with a set of fixed values? Why not just make it a `static` member (seeing as it's contents cannot change and aren't specific to the instance being constructed)? — CB Bailey, Apr 07 '13 at 12:08
Were it not for your last statement in the question, your query might have teeth, but as-written, Charles' comment addresses it pretty fundamentally. — WhozCraig, Apr 07 '13 at 12:15
You are right. Using static const member looks like a good idea. — Hubert Siwkin, Apr 07 '13 at 12:25

WhozCraig · Accepted Answer · 2013-04-07T12:38:18.270

The only way I can conceive doing this while staying out of the C++11 initializer list realm is to bury it in a struct wrapper and value-initialize it in your construct-initializer list:

#include <iostream>
using namespace std;

struct ArrayWrap
{
    int content[4];
    int& operator [](size_t n) { return content[n]; }
    int operator [](size_t n) const { return content[n]; }
};

static const ArrayWrap content = { {1,2,3,4} };


struct MyObj
{
    const ArrayWrap arrwrap;

    MyObj() : arrwrap(content) {}
};

int main(int argc, char *argv[])
{
    MyObj obj;
    for (int i=0;i<4;++i)
        cout << obj.arrwrap[i] << ' ';
    cout << endl;

    return EXIT_SUCCESS;
}

Output

1 2 3 4

It is common in C to bury fixed arrays in structures when returning them from functions by value, and in this case I'm simply exploiting the default copy-ctor of the wrapper struct as-generated by the C++ compiler.

Probably not the ideal solution for what you want, but it does work, and compiles under C++98.

score 0 · Answer 2 · edited May 23 '17 at 12:03

0

Well, if you're banning C++11 solutions from the candidate set, then you simply cannot do this.

edited May 23 '17 at 12:03

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answered Apr 07 '13 at 12:14

Lightness Races in Orbit

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it would be great if you could please tell us how to do it using c++11. – Saksham Apr 07 '13 at 12:39
@saksham: The question says `I want to avoid using -std=c++11 or -std=gnu++11.` – Lightness Races in Orbit Apr 07 '13 at 12:40
I know that but for my knowledge if you could – Saksham Apr 07 '13 at 12:41
1

@saksham: To do it using c++11 we just need to take advantage from initialization list. You have to declare a variable const int x[3] in declaration of a class 'A' in .hxx file. After that in .cpp file we have to write A() : x{1,2,3} {}, where A is a name of a class which stores x variable (so A() is a constuctor). I can send you an example class if this explanation wouldn't be sufficient. – Hubert Siwkin Apr 07 '13 at 13:51
@EjdzEs Thanks a lot! This is enough – Saksham Apr 07 '13 at 14:24
@saksham: Please, ask your own questions separately. – Lightness Races in Orbit Apr 07 '13 at 15:36

Initialization of const array in C++

2 Answers2