Why does setting the array to my class not work (operator overloading)?

[Flurite]

Hi,

As a general question, can arrays be set to other arrays? For example, this is my code:

// CLASS DEFINITION

class myClass
{
private:
    int m_array1[5];
public:
    operator int*();
};

// This is my operator overload

myClass::operator int*()
{
    return this->m_array1;
}

int main()
{
    myClass g;
    for (int i = 0; i < 5; i++)
    {
        int copyOfIterator = i;
        g[i] = ++copyOfIterator;
        cout << g[i] << "\n";
    }

    int* examplePointer1 = g; cout << "examplePointer1's first element is " << examplePointer1[0] << "\n";
    int exampleArray1[5]; exampleArray1 = g; cout << "exampleArray1's first element is " << exampleArray1[0] << "\n";

    return 0;
}

When I try to set exampleArray1 equal to class 'g', the compiler gives me an error, but when I set the pointer equal to class 'g', the compiler does not error. Why is this? Technically, I am setting a pointer to a pointer in both statements

[Athar]

You can't assign arrays to arrays (let alone assign pointers to arrays). Use std::vector instead.
The reason int* examplePointer1 = g; works is because you have a conversion operator to int*.

[Flurite]

Aren't arrays pointers themselves?

[Athar]

No, they're not. However, arrays can be implicitly converted to a pointer to their first element, which is why the following compiles:

int exampleArray1[5];
int* examplePointer1=exampleArray1;

[hanst99]

No, arrays are arrays. You usually refer to an array by a pointer to its first element though.

[Flurite]

So are arrays constant pointers that cannot change address? Is that the reason why I cannot set the address of the array pointer?

[Athar]

So are arrays constant pointers that cannot change address?

No, arrays are arrays like hanst99 said. A group of elements of the same type that are adjacent in memory.
There are C++ arrays (std::array in C++11 or boost::array) that encapsulate normal C arrays and can be used like a normal container (for example, you can assign them and iterate over them).

[vlad from moscow]

The title of the thread does not correspond to the discussion. In fact arrays can be set equal each other by copying elements of one array into another.:)

[Flurite]

Whether the array is a pointer to the first element or not, as long as its not const, I should be able to change what the pointer pointing to the first element of the array is pointing to.

[Athar]

Can't you read? An array is not a pointer.

[vlad from moscow]

Arrays can not be assigned. There is no such operation for arrays as the assignment exactly the same way as there is no such operation for example as the comparision (==) for arrays.
It is only then the name of an array takes part in an expression its name converted to a pointer of the first element of the array.

[Flurite]

@Arthar,

I was getting contradicting replies from you and hanst99.

@vlad from moscow,

Okay, I see. So how would one go about copying an array to another array? Looping through and inserting?

[vlad from moscow]

Yes. To assign one array to another means to copy elements from one array to another. You can use for example standard algorithm std::copy.

[Athar]

I was getting contradicting replies from you and hanst99.

No, we said the same thing.

Looping through and inserting?

Looping and assigning. However, no sane person would actually do this - that's what std::array and std::vector exist for.

[vlad from moscow]

In fact std::array uses the same copying element by element but thsi is done by the compiler when it performs assignment of one structure with the array to another.:)

[Flurite]

@Arthar,

hanst99 said:

"You usually refer to an array by a pointer to its first element though."

[vlad from moscow]

@Flurite
@Arthar,

hanst99 said:

"You usually refer to an array by a pointer to its first element though."

This means the word usually.

For example

int a[10];

int *p = a;

Another example

void print( char *s ) { std::cout << s << std::endl; }

char text[] = "This is some text";

print( text );

[Flurite]

Well, apparently this page says that an array is a constant pointer.

http://www.cplusplus.com/doc/tutorial/ntcs/

@vlad from moscow,

For the second example, is that a built-in C++ feature, and the character sequence is not technically an array?

[vlad from moscow]

No, array is array. As it is said in the C standard array is non-modifiable lvalue. Array is not a pointer.

And in the second example char text[] is array which initialized with string literal

[Athar]

Well, apparently this page says that an array is a constant pointer.

So it does, but it is incorrect. Don't take anything you read in tutorials at face value, stick to (reputable!) books or refer to the C++ standard directly. The confusion about this usually stems from the fact that an array can be implicitly converted to a pointer.