从 C# 调用 Windows API 函数时，应信任哪个签名源：.NET Framework 源代码还是 PInvoke？
例如，这是来自 .NET Framework 源文件UnsafeNativeMethods.cs：
[DllImport(ExternDll.User32, ExactSpelling=true, CharSet=CharSet.Auto)]
public static extern bool GetWindowRect(HandleRef hWnd,
[In, Out] ref NativeMethods.RECT rect);
这是来自 PInvoke.Net：
[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool GetWindowRect(HandleRef hwnd, out RECT lpRect);
哪个是此函数的正确/最佳签名？ （其中只有一个具有
[return: MarshalAs(UnmanagementType.Bool)]或[In, Out] ref等）我注意到在 .NET Framework 源文件中，许多/大多数签名都有
ExactSpelling=true, CharSet=CharSet.Auto，但在 PInvoke 上却没有。这是必需的吗？
For example, this is from .NET Framework source file UnsafeNativeMethods.cs:
[DllImport(ExternDll.User32, ExactSpelling=true, CharSet=CharSet.Auto)]
public static extern bool GetWindowRect(HandleRef hWnd,
[In, Out] ref NativeMethods.RECT rect);
and this is from PInvoke.Net:
[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool GetWindowRect(HandleRef hwnd, out RECT lpRect);
Which is the correct/best signature for this function? (only one of them has
[return: MarshalAs(UnmanagedType.Bool)], or[In, Out] ref, etc.)I've noticed that in .NET Framework source files many/most signatures have
ExactSpelling=true, CharSet=CharSet.Auto, but on PInvoke they don't. Is this required?
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他们都会完成工作。给pinvoke猫剥皮的方法不止一种。特别针对此示例：
ExactSpelling=true是一项优化，它避免 pinvoke 编组器查找GetWindowRectA和GetWindowRectW版本。对于这个特定的 API 函数来说，它们不存在，因为它不接受字符串参数。看到运行时的实际差异将是一个奇迹。CharSet=CharSet.Auto始终是一个好主意，因为默认值 (Ansi) 效率很低。它恰好在这里没有任何区别，因为该函数不接受任何字符串参数。[In, Out]是不必要的，因为这是 blittable 类型的默认值。这是一个昂贵的词，意味着 pinvoke 编组器可以直接传递指向托管内存的指针，不需要转换。尽可能高效。不过，与CharSet的想法相同，明确它有助于创建自记录代码并记住处理异常情况。只能使用[In]或[Out]可能是一项重大优化，但这里不适用，因为它已经优化了。 Fwiw，[Out] 是正确的选择。out与ref，与上面的想法相同。使用out更为正确，因为 API 实际上并不使用RECT内的任何传入值。然而，它在运行时没有任何区别，因为 JIT 编译器总是初始化一个结构。[return: MarshalAs(UnmanagedType.Bool)]是不必要的，它是 WindowsBOOL的默认封送处理。不知道为什么 pinvoke.net 总是包含它。简而言之，两者都不是完美的，但它们都可以工作。这就是pinvoke的危害。
They will both get the job done. There's just more than one way to skin a pinvoke cat. Specifically for this example:
ExactSpelling=trueis an optimization, it avoids having the pinvoke marshaller looking for theGetWindowRectAandGetWindowRectWversions. They don't exist for this particular API function since it doesn't take a string argument. Seeing an actual difference in run time would be a miracle.CharSet=CharSet.Autois always a good idea since the default (Ansi) is so inefficient. It just so happens to not make any difference here since the function doesn't take any string arguments.[In, Out]is unnecessary because that's the default for a blittable type. An expensive word that means that the pinvoke marshaller can directly pass a pointer to the managed memory, no conversion is required. As efficient as possible. Same idea asCharSetthough, being explicit about it helps to create self-documenting code and to remember to deal with the unusual case. Being able to only use[In]or[Out]can be a significant optimization, just not here since it is already optimized. Fwiw, [Out] would have been the correct choice.outvsref, same idea as above. Usingoutis more correct since the API doesn't actually use any passed-in values inside theRECT. It doesn't however make any difference at runtime since the JIT compiler always initializes a struct anyway.[return: MarshalAs(UnmanagedType.Bool)]is unnecessary, it is the default marshaling for a WindowsBOOL. Not sure why pinvoke.net always includes it.So in a nutshell, neither is perfect but they both will work. Such are the hazards of pinvoke.