CODEWITHSUNDEEP
c++arraysclassinitialization
Quade2002
Quade2002

Reputation: 653

How to initialize an array in C++ objects

After reading How to initialize an array in C, in particular:

Don't overlook the obvious solution, though:

int myArray[10] = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 };

I tried something like this:

#include <iostream>

class Something {
private:

int myArray[10];

public:

Something() {
    myArray[10] = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 };
}

int ShowThingy(int what) {
    return myArray[what];
}

~Something() {}
};

int main () {
   Something Thing;
    std::cerr << Thing.ShowThingy(3);
}

And I get:

..\src\Something.cpp: In constructor 'Something::Something()':
..\src\Something.cpp:10:48: error: cannot convert '<brace-enclosed initializer list>' to 'int' in assignment

The obvious in this case is not so obvious. I really would like the initiation of my array to be more dynamic as well.

I tired:

private:
    int * myArray;

public:
    Something() {
            myArray = new int [10];
            myArray = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 };
}

This looked funky to me to, and so to the compiler:

..\src\Something.cpp: In constructor 'Something::Something()':
..\src\Something.cpp:11:44: error: cannot convert '<brace-enclosed initializer list>' to 'int*' in assignment

This also did not work:

private:
int myArray[10] = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 };

with:

 ..\src\Something.cpp:6:20: error: a brace-enclosed initializer is not allowed here before '{' token
 ..\src\Something.cpp:6:51: sorry, unimplemented: non-static data member initializers
 ..\src\Something.cpp:6:51: error: 'constexpr' needed for in-class initialization of static data member 'myArray' of non-integral type

I have been doing really good and learning what does not work, but not so good learning what does work.

So, how do I used initialization lists {value, value, value} for an array inside a class?

I have been trying to figure out how to do this for some time now and am very stuck, I have a number of these kinds of lists I need to make for my app.

Upvotes: 18

Views: 108352

Answers (3)

Sunil Reddy
Sunil Reddy

Reputation: 1

It is possible to initialize array values of the array in size the main function like this:

Array *arr2 []= {{1, 3, 5, 6, 7},20,5};

Upvotes: -1

Praetorian
Praetorian

Reputation: 109089

You need to initialize the array in the constructor initialization list

#include <iostream>

class Something {
private:

int myArray[10];

public:

Something()
: myArray { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 }
{
}

int ShowThingy(int what) {
    return myArray[what];
}

~Something() {}
};

int main () {
   Something Thing;
    std::cerr << Thing.ShowThingy(3);
}

..\src\Something.cpp:6:51: sorry, unimplemented: non-static data member initializers

C++11 also adds supports for inline initialization of non-static member variables, but as the above error message states, your compiler has not implemented this yet.

Upvotes: 28

derekerdmann
derekerdmann

Reputation: 18252

Unless I'm mistaken, the initializer list is only allowed for when the variable is initialized during declaration - hence the name. You can't assign an initializer list to a variable, as you're trying to do in most of your examples.

In your last example, you're trying to add static initialization to a non-static member. If you want the array to be a static member of the class, you could try something like this: 

class Derp {
private:
    static int myArray[10];
}

Derp::myArray[] = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 };

If you want to add a class member, you could try making the static array const and copy it into the member array in the constructor.

Upvotes: 1

Related Questions