How to initialize vector from array without allocating more storage space?

Question

The direct way to initialize a vector from an array seems to be:

int sizeArr; int * array = getArray(sizeArr);
std::vector vec(array, array+sizeAr         


        

Answer 1

Why do you even allocate the memory with a pointer for int? There is a very high chance, that you have no reason for doing this.

If you have a compiler which assists c++11 it should be possible to just initialize the vector with std::vector vec{array}; Or if you dont need the array anymore, just delete it and push references of the array to the vector

Answer 2

If the caller doesn't own the data (i.e. is not in charge of deleting it), then the easiest option might be to write a container-like wrapper:

template <typename T>
struct array_wrapper
{
  typedef T* iterator;
  typedef const T* const_iterator;
  array_wrapper(T* begin, T* end) : data_(begin), size_(end-begin) {}
  iterator begin() { return data_; }
  iterator end() { return data_ + size_; }
  const_iterator begin() const { return data_; }
  const_iterator end() const { return data_ + size_; }
  size_t size() const { return size_; }
  T& operator[](size_t i) { return _data[i]; }
  const T& operator[](size_t i) const { return _data[i]; }
  void swap(array_wrapper& other) { 
    std::swap(size_, other.size_);
    std::swap(data_, other.data_);
  }
 private:
  T* data_;
  size_t size_;
};

then

array_wrapper<int> vec(array, array+sizeArr);

This has a lot of the functionality of an std::vector, but does not own the underlying data, and supports no operations that would result in resizing or re-allocating.