class Fiddle::CStructEntity

A pointer to a C structure

Public Class Methods

alignment(types) click to toggle source

# File fiddle/lib/fiddle/struct.rb, line 277
def CStructEntity.alignment(types)
  max = 1
  types.each do |type, count = 1|
    if type.respond_to?(:entity_class)
      n = type.alignment
    else
      n = ALIGN_MAP[type]
    end
    max = n if n > max
  end
  max
end

malloc(types, func = nil, size = size(types)) { |struct| ... } click to toggle source

Allocates a C struct with the types provided.

See Fiddle::Pointer.malloc for memory management issues.

Calls superclass method Fiddle::Pointer::malloc

# File fiddle/lib/fiddle/struct.rb, line 293
def CStructEntity.malloc(types, func = nil, size = size(types), &block)
  if block_given?
    super(size, func) do |struct|
      struct.set_ctypes types
      yield struct
    end
  else
    struct = super(size, func)
    struct.set_ctypes types
    struct
  end
end

new(addr, types, func = nil) click to toggle source

Wraps the C pointer addr as a C struct with the given types.

When the instance is garbage collected, the C function func is called.

Public Instance Methods

[](*args) click to toggle source

Fetch struct member name if only one argument is specified. If two arguments are specified, the first is an offset and the second is a length and this method returns the string of length bytes beginning at offset.

Examples:

my_struct = struct(['int id']).malloc
my_struct.id = 1
my_struct['id'] # => 1
my_struct[0, 4] # => "\x01\x00\x00\x00".b

Calls superclass method Fiddle::Pointer::[]

# File fiddle/lib/fiddle/struct.rb, line 413
def [](*args)
  return super(*args) if args.size > 1
  name = args[0]
  idx = @members.index(name)
  if( idx.nil? )
    raise(ArgumentError, "no such member: #{name}")
  end
  ty = @ctypes[idx]
  if( ty.is_a?(Array) )
    if ty.first.respond_to?(:entity_class)
      return @nested_structs[name]
    else
      r = super(@offset[idx], SIZE_MAP[ty[0]] * ty[1])
    end
  elsif ty.respond_to?(:entity_class)
    return @nested_structs[name]
  else
    r = super(@offset[idx], SIZE_MAP[ty.abs])
  end
  packer = Packer.new([ty])
  val = packer.unpack([r])
  case ty
  when Array
    case ty[0]
    when TYPE_VOIDP
      val = val.collect{|v| Pointer.new(v)}
    end
  when TYPE_VOIDP
    val = Pointer.new(val[0])
  else
    val = val[0]
  end
  if( ty.is_a?(Integer) && (ty < 0) )
    return unsigned_value(val, ty)
  elsif( ty.is_a?(Array) && (ty[0] < 0) )
    return StructArray.new(self + @offset[idx], ty[0], val)
  else
    return val
  end
end

[]=(*args) click to toggle source

Set struct member name, to value val. If more arguments are specified, writes the string of bytes to the memory at the given offset and length.

Examples:

my_struct = struct(['int id']).malloc
my_struct['id'] = 1
my_struct[0, 4] = "\x01\x00\x00\x00".b
my_struct.id # => 1

Calls superclass method Fiddle::Pointer#[]=

# File fiddle/lib/fiddle/struct.rb, line 465
def []=(*args)
  return super(*args) if args.size > 2
  name, val = *args
  name = name.to_s if name.is_a?(Symbol)
  nested_struct = @nested_structs[name]
  if nested_struct
    if nested_struct.is_a?(StructArray)
      if val.nil?
        nested_struct.each do |s|
          s.replace(nil)
        end
      else
        val.each_with_index do |v, i|
          nested_struct[i] = v
        end
      end
    else
      nested_struct.replace(val)
    end
    return val
  end
  idx = @members.index(name)
  if( idx.nil? )
    raise(ArgumentError, "no such member: #{name}")
  end
  ty  = @ctypes[idx]
  packer = Packer.new([ty])
  val = wrap_arg(val, ty, [])
  buff = packer.pack([val].flatten())
  super(@offset[idx], buff.size, buff)
  if( ty.is_a?(Integer) && (ty < 0) )
    return unsigned_value(val, ty)
  elsif( ty.is_a?(Array) && (ty[0] < 0) )
    return val.collect{|v| unsigned_value(v,ty[0])}
  else
    return val
  end
end

assign_names(members) click to toggle source

Set the names of the members in this C struct

# File fiddle/lib/fiddle/struct.rb, line 349
def assign_names(members)
  @members = []
  @nested_structs = {}
  members.each_with_index do |member, index|
    if member.is_a?(Array) # nested struct
      member_name = member[0]
      struct_type, struct_count = @ctypes[index]
      if struct_count.nil?
        struct = struct_type.new(to_i + @offset[index])
      else
        structs = struct_count.times.map do |i|
          struct_type.new(to_i + @offset[index] + i * struct_type.size)
        end
        struct = StructArray.new(to_i + @offset[index],
                                 struct_type,
                                 structs)
      end
      @nested_structs[member_name] = struct
    else
      member_name = member
    end
    @members << member_name
  end
end

set_ctypes(types) click to toggle source

Calculates the offsets and sizes for the given types in the struct.

# File fiddle/lib/fiddle/struct.rb, line 375
def set_ctypes(types)
  @ctypes = types
  @offset = []
  offset = 0

  max_align = types.map { |type, count = 1|
    orig_offset = offset
    if type.respond_to?(:entity_class)
      align = type.alignment
      type_size = type.size
    else
      align = ALIGN_MAP[type]
      type_size = SIZE_MAP[type]
    end
    offset = PackInfo.align(orig_offset, align)

    @offset << offset

    offset += (type_size * count)

    align
  }.max

  @size = PackInfo.align(offset, max_align)
end