[英]IntPtr and avoiding unsafe code
I have an external library that takes an IntPtr. 我有一个带IntPtr的外部库。 Is there any safe way to do this...
有没有安全的方法来做到这一点......
int BytesWritten = 0;
Output.WriteBytes(buffer, new IntPtr(&BytesWritten));
...without having to use 'unsafe' code? ...而不必使用'不安全'代码? I'm not that familiar with IntPtrs, but I'd like to do something like this:
我对IntPtrs并不熟悉,但我想做这样的事情:
fixed int BytesWritten = 0;
Output.WriteBytes(buffer, IntPtr.GetSafeIntPtr(ref BytesWritten));
...in such a way that I don't need to compile with /unsafe. ......以这种方式我不需要编译/不安全。
I can't change the WriteBytes function, it's an external function. 我不能改变WriteBytes函数,它是一个外部函数。
It seems like there should be some sort of cast between 'ref int' and IntPtr, but I have not had luck finding it. 似乎应该在'ref int'和IntPtr之间进行某种转换,但我没有找到它的运气。
Yes, there is. 就在这里。 You can use P/Invoke for your code.
您可以使用P / Invoke代码。 It will create the pointer for you automagically.
它会自动为您创建指针。 Something like this:
像这样的东西:
[DllImport("yourlib", SetLastError=true)]
static extern bool WriteBytes(
[MarshalAs(UnmanagedType.LPArray)]
byte [] buffer,
ref int BytesWritten);
(I added the array as a bonus) . (我添加了阵列作为奖励) 。 More info on P/Invoke can be found, with gazillion examples, at pinvoke.net .
有关P / Invoke的更多信息,可以在pinvoke.net找到很多例子。
Each parameter above can take out
, in
and ref
. 上面的每个参数都可以
out
, in
和ref
。 Out and ref parameters are translated as pointers, where an ref-parameter is two-way. Out和ref参数被转换为指针,其中ref参数是双向的。
I assume that Output.WriteBytes
is a [DllImport]
method. 我假设
Output.WriteBytes
是[DllImport]
方法。 Can you post the declaration? 你可以发表声明吗?
You should be able to avoid the pointer by declaring the last parameter as out int
instead of IntPtr
-- let the P/Invoke marshaller do the rest. 你应该能够通过将最后一个参数声明为
out int
而不是IntPtr
来避免指针 - 让P / Invoke marshaller完成剩下的工作。
Here is a class that will provide you with a safe IntPtr implementation. 这是一个为您提供安全的IntPtr实现的类。 It derives from the SafeHandleZeroOrMinusOneIsInvalid class, provided by the .NET framework.
它派生自.NET框架提供的SafeHandleZeroOrMinusOneIsInvalid类。
/// <summary>
/// IntPtr wrapper which can be used as result of
/// Marshal.AllocHGlobal operation.
/// Call Marshal.FreeHGlobal when disposed or finalized.
/// </summary>
class HGlobalSafeHandle : SafeHandleZeroOrMinusOneIsInvalid
{
/// <summary>
/// Creates new instance with given IntPtr value
/// </summary>
public HGlobalSafeHandle(IntPtr ptr) : base(ptr, true)
{
}
/// <summary>
/// Creates new instance with zero IntPtr
/// </summary>
public HGlobalSafeHandle() : base(IntPtr.Zero, true)
{
}
/// <summary>
/// Creates new instance which allocates unmanaged memory of given size
/// Can throw OutOfMemoryException
/// </summary>
public HGlobalSafeHandle(int size) :
base(Marshal.AllocHGlobal(size), true)
{
}
/// <summary>
/// Allows to assign IntPtr to HGlobalSafeHandle
/// </summary>
public static implicit operator HGlobalSafeHandle(IntPtr ptr)
{
return new HGlobalSafeHandle(ptr);
}
/// <summary>
/// Allows to use HGlobalSafeHandle as IntPtr
/// </summary>
public static implicit operator IntPtr(HGlobalSafeHandle h)
{
return h.handle;
}
/// <summary>
/// Called when object is disposed or finalized.
/// </summary>
override protected bool ReleaseHandle()
{
Marshal.FreeHGlobal(handle);
return true;
}
/// <summary>
/// Defines invalid (null) handle value.
/// </summary>
public override bool IsInvalid
{
get
{
return (handle == IntPtr.Zero);
}
}
}
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