C/C++ private array initialization in the header file

Question

I have a class called Cal and it's .cpp and .h counterpart

Headerfile has

class Cal {
    private:
        int wa[2][2];

    public:
        void do_cal();
};

.cpp file has

#include "Cal.h"
void Cal::do_cal() {
   print(wa) // where print just itterates and prints the elements in wa
}

My question is how do I initialize the array wa ? I just can't seem to get it to work.

I tried with :

int wa[2][2] = {
                {5,2},
                {7,9}
               };

in the header file but I get errors saying I cant do so as it's against iso..something.

Tried also to initialize the array wa in the constructor but that didnt work either.. What am I missing ?

Thanks

Answer 1

You cannot initialize array elements in a class declaration. I recently tried to find a way to do just that. From what I learned, you have to do it in your initialize function, one element at a time.

Cal::Cal{
   wa[0][0] = 5;
   wa[0][1] = 2;
   wa[1][0] = 7;
   wa[1][1] = 9;
}

It's possible (and probable) that there's a much better way to do this, but from my research last week, this is how to do it with a multi dimensional array. I'm interested if anyone has a better method.

Answer 2

You can't do it easily. If you don't want to specify each element individually like in Perchik's answer, you can create one static array and memcpy that (which will probably be faster for non-trivial array sizes):

namespace
{
    const int default_wa[2][2] = {{5, 2}, {7, 9}};
}

Cal::Cal
{
    memcpy(&wa[0][0], &default_wa[0][0], sizeof(wa));
}

Answer 3

If it can be static, you can initialize it in your .cpp file. Add the static keyword in the class declaration:

class Cal {
    private:
        static int wa[2][2];
    public:
        void do_cal();
};

and at file scope in the .cpp file add:

#include "Cal.h"
int Cal::wa[2][2] = { {5,2}, {7,9} };
void Cal::do_cal() {
   print(wa) // where print just itterates and prints the elements in wa
}

If you never change it, this would work well (along with making it const). You only get one that's shared with each instance of your class though.

Answer 4

I've declare my variables in header file just like:

const char lettr[3];
const int st_end[3][2];

and wanto initialize them in cpp file:

char AbcDlg::lettr[3]={'A','B','C'};
int AbcDlg::st_end[3][2]={{0,16},{2,14},{6,10}};

what's the problem??? the error got from compiler is:

Error 1 error C2439: 'AbcDlg::lettr' : member could not be initialized c:\documents and settings\admin\desktop\abc\abc\abc\abcdlg.cpp 52 Error 3 error C2439: 'AbcDlg::list' : member could not be initialized c:\documents and settings\admin\desktop\abc\abc\abc\abcdlg.cpp 52 Error 2 error C2439: 'AbcDlg::st_end' : member could not be initialized c:\documents and settings\admin\desktop\abc\abc\abc\abcdlg.cpp 52 Error 4 error C2761: 'const char AbcDlg::lettr[3]' : member function redeclaration not allowed c:\documents and settings\admin\desktop\abc\abc\abc\abcdlg.cpp 163 Error 5 fatal error C1903: unable to recover from previous error(s); stopping compilation c:\documents and settings\admin\desktop\abc\abc\abc\abcdlg.cpp 163

PLZ help how can i initialize them???