How to get the address of the std::vector buffer start most elegantly?

Question

I want to use std::vector for dynamically allocating memory. The scenario is:

int neededLength = computeLength(); // some logic here

// this will allocate t         


        

Answer 1

For functions like these, I use a utility class, SizedPtr that basically holds a pointer and an element count. A set of converter functions creates the SizedPtr from different inputs. So the call changes to:

vector foo;
callFunction(sizedptr(foo));

One could even add an implicit std::vector constructor to SizedPtr, but I wanted to avoid this dependency.

This helps only if callFunction is under your control. It is a pleasure to work with, if you work with different vector types in one application and you want to consolidate. If you generally work with std::vector, it's mostly pointless.

Roughly:

template
class SizedPtr
{
    T * m_ptr;
    size_t m_size;
  public:
    SizedPtr(T* p, size_t size) : ... {}
    T * ptr() { return m_ptr; }
    size_t size() const { return m_size; }

   // index access, STL container interface, Sub-Sequence, ...

}

The idea behind this is to separate the operation - manipulating a contiguous sequence of elements - from the storage (std::vector). It's similar to what STL does with iterators, but avoids template infection.