Question

I have been writing C++ for a little while (java/C for a long while), I am wondering if there is a trick I don’t know which can help me do the following.

vector<unsigned char> *fromArray(unsigned char data[], int length)
{
    vector<unsigned char> *ret = new vector<unsigned char >();
    while (length--)
    {
        ret->push_back(*data);
    }
    return ret;
}

And you can use it like so:

unsigned char tmp[] = {0, 1, 2, 3, 4, 5};
vector<unsigned char> *a = fromArray(tmp, sizeof(tmp));
// use `a' here

I find that pretty cumbersome – I’d like to write it all on one line

vector<unsigned char> *a = fromArray({0, 1, 2, 3, 4, 5});
// use `a' here

Is such a thing possible? I don’t have access to C++11 unfortunately (looks like its initializer_list is exactly what I want).

EDIT

Sorry I had some of the fundamentals wrong in here. I will now avoid extending std::vector. However I think the question is still valid, just that my example was a bad one.

** Potential workaround **

I could define a bunch of overloaded functions to take different numbers of arguments, eg

vector<unsigned char> *fromArray(unsigned char a)
{
    vector<unsigned char> *ret = new vector<unsigned char >();
    ret->push_back(a);
    return ret;
}

vector<unsigned char> *fromArray(unsigned char a, unsigned char b)
{
    vector<unsigned char> *ret = new vector<unsigned char >();
    ret->push_back(a);
    ret->push_back(b);
    return ret;
}

But I don’t think I will bother…

Answer 1

You can use a template to deduce the size of any fixed size array:

template< class T, size_t N >
auto_ptr<ByteArray> foo( T (&data)[N] )
{
  return auto_ptr<ByteArray>(new ByteArray(data, N));
}

then

unsigned char tmp[] = {0, 1, 2, 3, 4, 5};
auto_ptr<ByteArray> a = foo(tmp);

But bear in mind that auto_ptr is deprecated. Prefer unique_ptr. Also, note you should not publicly inherit from std::vector.