Is there a random access container type that accepts a prefilled & preallocated buffer?

Question

I'm about to write something myself since I didn't find what I was looking for, but figured I should ask the crowd before diving in.

• Is there a boost or stl random access container type that allows passing in of prefilled buffer?

The imaginary(?) container type would operate something like this:

  const int blobSize = unpackBlobSize( msg );
  int *     blob     = unpackBlobData( msg );

  SpecialVector<int> mySpecialIntVector( blob, blobSize );

Basically I'm interfacing an old library with c-style raw pointers-to-buffers, but would like to use C++ style container semantics without requiring a copy step. What I would hope to have is std::vector plus preallocated & prefilled buffer constructor and, minus resize.

Libeigen has this sort of functionality with their Eigen::Map which allows things like the following:

  int array[9];
  for(int i = 0; i < 9; ++i) 
      array[i] = i;
  stl::cout << Eigen::Map<Eigen::Matrix3i>(array) << stl::endl;

Anyone know of a boost or stl template that covers these constraints?

Answer 1

Going from Dennis Zickenfoose's comment, I looked up Boost.range seems to offer the perfect solution:

  #include <boost/range.hpp>
  #include <boost/foreach.hpp>
  #include <iostream>

  int main()
  {
    const int blobSize = 100;
    int blob[blobSize];

    for( int i = 0; i < blobSize; ++i )
      blob[i] = i;

    boost::iterator_range<int*> blobPsudoContainer( blob, blob + blobSize );

    BOOST_FOREACH( int & i, blobPsudoContainer )
      i = i + 1;

    std::cout << "Size is:" << blobPsudoContainer.size() << "\n";
    std::cout << "value at 0 is:" << blobPsudoContainer[0] << "\n";
    return 0;
  }

Thanks Dennis! : )

Answer 2

There's nothing like you want, this is just a shortcoming of the language. If you were satisfied with having the allocator statically guess a good expected maximum element count, you could just embed a normal C array inside an allocator and defer to it as long as possible; this is usually called an auto buffer.

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Old Answer:

All of the standard library containers allow you to specify an allocator. You can make a buffer allocator.