CODEWITHSUNDEEP
c++templatesreference
Aviv Cohn
Aviv Cohn

Reputation: 17183

'invalid conversion from int to int*'

I have a template class template <typename T> class SomeClass. It has a member T* data[10], and a method:

void add(const T& item){
    data[indexToInsert++] = item;
}

In main(), there is the following code:

SomeClass<int> container;
container.add(10);

On the second line, I get this error:

invalid conversion from int to int*

I don't understand why I get this error. The integer 10 is passed as const reference to add(). Then, as a const reference, it's assigned to an array of pointers.

Either some of my assumptions are wrong (for example, is T* data[10] actually an array of pointers?), or something that I think should work doesn't.

Please explain the technical reasons to why this fails and how to fix it.

Upvotes: 0

Views: 1249

Answers (2)

Felix Glas
Felix Glas

Reputation: 15524

The member data is declared as an array of T*, i.e. an array of pointers as you said yourself.

T* data[10] // 'data' is an array of T*.

To declare an array of T use:

T data[10]; // 'data' is an array of T.

You get the error because you are trying to assign an int to an array element of type int*. Signed integers are not implicitly convertible to addresses/pointers.

Also remember that a reference is basically an alias of an object i.e. it behaves as if you pass the object itself but with reference semantics. You can not assign a reference to a pointer, but you can assign a reference to an object.

Example

int  i = 5;
int& r = i;  // Reference to 'i';
int* p = &i; // Pointer to 'i'.

std::cout << r << std::endl; // Outputs '5'.
std::cout << p << std::endl; // Outputs the address of 'i'.

Upvotes: 2

d3coy
d3coy

Reputation: 395

You hit the nail on the head: T* data[10] is an array of pointers.

Change your member array to:

T data[10];

...and you'll be fine.

Upvotes: 0

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