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up vote 1 down vote favorite

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...

share|improve this question
2  
What's wrong with std::vector ? –  us2012 Feb 11 '13 at 22:45
    
nothing :) in actual code this class extends std::vector, adds methods for printing, and convenience functions for constructing –  Wayne Uroda Feb 11 '13 at 22:46
1  
"Methods for printing" doesn't sound like a job for extending the vector class, more like you should use non-member functions for that. –  us2012 Feb 11 '13 at 22:48
    
I do actually use a non member function to overload the << stream operator. –  Wayne Uroda Feb 11 '13 at 22:50

1 Answer 1

up vote 1 down vote accepted

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.

share|improve this answer
    
I will try this, thanks. As I said, I don't have access to C++11. and I don't really want to use Boost (rather, it isn't fully available on my platform). –  Wayne Uroda Feb 11 '13 at 22:49
    
What's wrong with publicly inheriting from std::vector? –  Wayne Uroda Feb 11 '13 at 22:51
    
@WayneUroda it is not designed for that. It doesn't have a virtual destructor, which means you get undefined behaviour if you are deleting an object of the derived type from a pointer to the base. –  juanchopanza Feb 11 '13 at 22:54
    
So I should not inherit from it at all, or is private inheritance safe? –  Wayne Uroda Feb 11 '13 at 22:59
    
@WayneUroda it is controversial. Private inheritance is almost safe, there are some pathological cases where it may cause trouble. The preferred option these days is containment. See this article for more info. –  juanchopanza Feb 11 '13 at 23:02

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