Question

I have tried to create a template function that does some weighted sampling within a Monte Carlo simulation. It is below. input_data will either be a statically-allocated array (i.e. data[33]), a dynamically-allocated array, or a vector.

template <class myType>
int init_roulette_calcs(myType &input_data, int inputlength, int *(&output_cdf), int highclassix, int weight)
{
        sort(input_data, input_data + inputlength); //where the error occurs

        //other code:
        output_cdf = new int [inputlength];
        int k = 1;
    for (int i = 0; i < inputlength; i++)
    {
        output_cdf[i] = k;
        if (i+1 < highclassix) k++;
        else    k += weight;
    }
    return output_cdf[inputlength-1];
}

The code will not compile because the template function could not deduce the argument for the call to sort. This may be a stupid question, but what do I need to do to ensure that sort can work properly?

Error   4   error C2784: 'std::_Vb_iterator<_Alloc> std::operator 
+(_Alloc::difference_type,std::_Vb_iterator<_Alloc>)' : could not deduce template argument for 
'std::_Vb_iterator<_Alloc>' from 'int'  j:\rdm\lrgv_2011-07-21\lrgv_src\lrgv.h  398

Thanks in advance for your help.

Answer 1

If you put in an array, the array name is essentially a pointer to the first element, and the array name + x is the poitner to the xth element – so you have this part correct.

The problem is that this is not the case for a vector, which is why you need to use the .begin() and .end() functions to get the pointer to these locations.

You could try sorting by pulling the addresses of the dereferenced start/end elements – that might let you treat a vector the same as an array.