Ruby FFI：指向无符号整数数组的指针答案

【问题标题】：Ruby FFI: Pointer to an array of unsigned integerRuby FFI：指向无符号整数数组的指针
【发布时间】：2014-05-12 08:49:24
【问题描述】：

我正在尝试在我的 ruby 程序中使用 EnumProcesses：

BOOL WINAPI EnumProcesses(
  _Out_  DWORD *pProcessIds,
  _In_   DWORD cb,
  _Out_  DWORD *pBytesReturned
);

我需要定义一个指向无符号整数数组的指针，我这样做的方式如下：

require 'ffi'

module Win32
  extend FFI::Library
  ffi_lib 'Psapi'
  ffi_convention :stdcall
  attach_function :EnumProcesses,  [:pointer, :uint, :pointer], :int
end

process_ids    = FFI::MemoryPointer.new(:uint, 1024)
bytes_returned = FFI::MemoryPointer.new(:uint)

if Win32.EnumProcesses(process_ids, process_ids.size, bytes_returned) != 0
  puts bytes_returned.read_string
end

上面返回的字节的输出是一种像x☺这样的垃圾字符

让我知道我哪里做错了？

【问题讨论】：

标签： c ruby winapi process ffi

【解决方案1】：

你们很亲密。主要问题是解释从 Microsoft 返回的数据。它不是一个字符串。它是一个 DWORD 或 uint32 数组。

试一试：

require 'ffi'

module Win32

  extend FFI::Library
  ffi_lib 'Psapi'
  ffi_convention :stdcall

=begin
  BOOL WINAPI EnumProcesses(
    _Out_  DWORD *pProcessIds,
    _In_   DWORD cb,
    _Out_  DWORD *pBytesReturned
  );
=end
  attach_function :EnumProcesses, [:pointer, :uint32, :pointer], :int

end

# Allocate room for the windows process ids.
process_ids = FFI::MemoryPointer.new(:uint32, 1024)

# Allocate room for windows to tell us how many process ids there were.
bytes_returned = FFI::MemoryPointer.new(:uint32)

# Ask for the process ids
if Win32.EnumProcesses(process_ids, process_ids.size, bytes_returned) != 0

  # Determine the number of ids we were given
  process_ids_returned = bytes_returned.read_int / bytes_returned.size

  # Pull all the ids out of the raw memory and into a local ruby array.
  ids = process_ids.read_array_of_type(:uint32, :read_uint32, process_ids_returned)

  puts ids.sort
end

【讨论】：