为什么在 DllImport 返回值中用 IntPtr 或 StringBuilder 替换 char[] 会导致我的程序不再找到正确的入口点？

发布于 2024-08-11 21:39:08 字数 859 浏览 6 评论 0原文

编辑：我刚刚意识到这是定义为宏，而不是函数。我到底如何将宏从 DLL 导入到 C# 中？（这可能是一个新问题）。

这与我刚刚问的一个问题有关：

我该怎么办正确地将字符从非托管 Dll 返回到 C#？

一些答案建议我将函数签名更改为 IntPtr 或 StringBuilder。我还在谷歌搜索的一些网站上看到了这些解决方案，最值得注意的是这里。（还有其他的，但我没有时间寻找链接）。

函数签名：

[DllImport("api.dll")]       
internal static extern char[] errMessage(int err);

如果我更改返回类型，我的调用将引发以下异常：

“无法在 DLL 中找到名为“errMessage”的入口点”

如果它不起作用，我无法想象人们会建议这样做。我在这里做错了什么吗？是不是少了点什么？遗憾的是，我的 C/C++ 技能很糟糕，所以我可能会错过一些非常简单的东西。感谢您的任何帮助。

编辑：文档中的函数签名：

char * errMessage(int err);

原文

EDIT: I just realized this is defined as a MACRO, not a function. How the heck would I import a macro from a DLL to C#? (this may have to be a new question).

This is related to a question I just asked:

How Do I Properly Return A Char From An Unmanaged Dll To C#?

Some of the answers suggested I change the function signature to IntPtr or StringBuilder. I also saw these solutions on a few sites in my googling, most notably here. (There were others, but I don't have time to hunt down the links).

Function signature:

[DllImport("api.dll")]       
internal static extern char[] errMessage(int err);

If I change the return type, my call throws the following exception:

"Unable to find an entry point named 'errMessage' in DLL"

I can't imagine people would suggest this if it didn't work. Am I doing something wrong here? Is there something missing? Sad to say, but my C/C++ skills are terrible, so I could be missing something really simple. Thanks for any help.

EDIT: Function signature from documentation:

char * errMessage(int err);

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放血 2024-08-18 21:39:08

编写 C++/CLI 包装器。这是一种弥合 C# 和非托管（旧）C/C++ 之间差距的极其简单且强大的方法。

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不爱素颜 2024-08-18 21:39:08

编辑：更新以反映导入宏：

你不能。

现在，你可以做的是查看宏的作用，然后使用 P/Invoke 实现它。以下建议也适用于此。

使用 Platform Invoke (P/Invoke) 时，最好尽可能明确：

internal static class NativeMethods
{
    private static string DllName = @"api.dll";

    // This uses 'string' assuming you do not have to free the memory.
    [DllImport(DllName, EntryPoint = "errMessage",
         CharSet = YourCharacterSet,              // CharSet.Ansi? .Unicode?
         CallingConvention = DllCallingConvention // .StdCall? .Cdecl?
    )]
    public static string errMessage(int errorCode);
}

此外，最好提供一个托管入口点，使该方法更加“.Net”。您可以在此处确保调用者分配的内存保持适当的时间（您可能必须实现 SafeHandle) 或其他挥手动作得到处理。

假设 errMessage 返回一个字符串，我们不负责释放：

public static class ManagedMethods
{
    public static string ErrorMessage(ErrorCode errorCode)
    {
        return NativeMethods.errMessage((int)errorCode);
    }
}

EDIT: updated to reflect importing a macro:

You can't.

Now, what you can do is look at what the macro does, then implement that with P/Invoke. The below advice holds for that as well.

When working with Platform Invoke (P/Invoke) it is best to be as explicit as possible:

internal static class NativeMethods
{
    private static string DllName = @"api.dll";

    // This uses 'string' assuming you do not have to free the memory.
    [DllImport(DllName, EntryPoint = "errMessage",
         CharSet = YourCharacterSet,              // CharSet.Ansi? .Unicode?
         CallingConvention = DllCallingConvention // .StdCall? .Cdecl?
    )]
    public static string errMessage(int errorCode);
}

Moreover, it is best to provide a managed entry-point that makes the method more ".Net". This is where you would ensure that Caller allocated memory gets held the appropriate amount of time (you may have to implement a SafeHandle) or that other hand-waving gets handled.

Assuming errMessage returns a string we aren't responsible for deallocating:

public static class ManagedMethods
{
    public static string ErrorMessage(ErrorCode errorCode)
    {
        return NativeMethods.errMessage((int)errorCode);
    }
}

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