Feature request read_array_of_struct or How to use ruby FFI to read array of static structures

[kojix2]

Hi!
Question and Feature request.

I searched Internet and found this answer.
How to use ruby FFI to read array of static structures

There's no particularly nice way, I'm afraid. read_array_of_type doesn't work for structs.

You can achieve this using simple pointer arithmetics:

def self.readDataArray
    pointer = myData
    array_of_structs = 3.times.map { |idx| 
        MyStruct.new(pointer + idx * MyStruct.size)
    }
    # Do your business
end

Yes. It works well. But, I think it would be nice to have methods like

• read_array_of_struct
• get_array_of_struct

module FFI
  class Pointer
    def read_array_of_struct(type, length)
      ary = []
      size = type.size
      tmp = self
      length.times { |j|
        ary << type.new(tmp)
        tmp += size unless j == length-1 # avoid OOB
      }
      ary
    end unless method_defined?(:read_array_of_struct)
  end
end

Usage

array = memory.read_array_of_struct(Foo::FFI::Bar, 3) 
# => [#<BAR>, #<BAR>, #<BAR>]

We have read_array_of_type. But it is not what I am looking for.

ffi/lib/ffi/pointer.rb

Lines 107 to 123 in 2cc0e53

	# @param [Type] type type of data to read from pointer's contents
	# @param [Symbol] reader method to send to +self+ to read +type+
	# @param [Numeric] length
	# @return [Array]
	# Read an array of +type+ of length +length+.
	# @example
	# ptr.read_array_of_type(TYPE_UINT8, :read_uint8, 4) # -> [1, 2, 3, 4]
	def read_array_of_type(type, reader, length)
	ary = []
	size = FFI.type_size(type)
	tmp = self
	length.times { |j|
	ary << tmp.send(reader)
	tmp += size unless j == length-1 # avoid OOB
	}
	ary
	end unless method_defined?(:read_array_of_type)

Perhaps I missed a useful feature of ruby-ffi. If so, I'd be glad to know.

Thank you.