[C++] Add convenience method to construct Buffer from a string that owns its memory

[asfimport]

The memory would need to be allocated from a memory pool / buffer allocator

Reporter: Wes McKinney / @wesm
Assignee: Panchen Xue / @xuepanchen

PRs and other links:

• GitHub Pull Request #1518

_{Note: This issue was originally created as ARROW-1623. Please see the migration documentation for further details.}

[asfimport]

Panchen Xue / @xuepanchen:
Is this for base class Buffer or derived PoolBuffer?

[asfimport]

Uwe Korn / @xhochy:
This is for the base class Buffer. PoolBuffer owns it's memory directly where the method to be implemented here will use memory that is owned by a string instance.

[asfimport]

Wes McKinney / @wesm:
The API would be something like

Status Buffer::FromString(const std::string& value, MemoryPool* pool, std::shared_ptr<Buffer>* out)

[asfimport]

Panchen Xue / @xuepanchen:
My understanding is:

Status Buffer::FromString(const std::string& data, MemoryPool* pool, std::shared_ptr<Buffer>* out) const {
  auto new_buffer = std::make_shared<PoolBuffer>(pool);
  auto size = static_cast<int64_t>(data.size());
  auto str = reinterpret_cast<const uint8_t*>(data.c_str());

  RETURN_NOT_OK(new_buffer->Resize(size));
  std::memcpy(new_buffer->mutable_data(), str, size);

  *out = new_buffer;
  return Status::OK();
}

Is it correct? Or shall we change the calling object?

[asfimport]

Wes McKinney / @wesm:
Yes, a static member function would be fine. You can use AllocateBuffer to save a line of code

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1518
#1518