将 C# 中的数组和指针与 C DLL 一起使用
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Using arrays and pointers in C# with C DLL
提问by
I am very new to C# (just started learning in the past week).
我对 C# 很陌生（上周才开始学习）。
I have a custom DLL written in C with the following function:
我有一个用 C 编写的自定义 DLL，具有以下功能：
DLLIMPORT void test_function (double **test)
What I am looking to do is have a pointer from C# for the array 'test'.
我想要做的是有一个来自 C# 的指针，用于数组“test”。
So, if in the DLL function I have test[0] = 450.60, test[1] = 512.99 etc. I want to be able to have that available in my C# program.
因此，如果在 DLL 函数中我有 test[0] = 450.60、test[1] = 512.99 等。我希望能够在我的 C# 程序中使用它。
In the C# program I have something similar to:
在 C# 程序中，我有类似的东西：
namespace TestUtil
{
public class Echo
{
public double[] results = new double[10];
public double[] results_cpy = new double[10];
[DllImport("test_dll.dll", CallingConvention = CallingConvention.Cdecl)]
static extern unsafe void test_function(ref double[] Result);
public unsafe void Tell()
{
results[0] = 0.0;
results[1] = 0.0;
results_cpy[0] = 0.0;
results_cpy[1] = 0.0;
test_function(ref results);
results_cpy[0] = (double)results[0] + (double)results[1] ;
}
}
}
In the DLL's 'test_function' function I used the following:
在 DLL 的“test_function”函数中，我使用了以下内容：
*test[0] = 450.60;
*test[1] = 512.99;
Within the DLL everything was OK (I used a message box within the DLL to check the values were being applied). Back in the C# program 'results[0]' appears to be fine and I can get values from it, but 'results[1]' gives me an index out of bounds error. I know this because if I omit '+ (double)results[1]' I receive no error. Also, if I make no attempt within the DLL to modify 'test[1]' it retains the original value from C# (in my example 0.0).
在 DLL 中一切正常（我在 DLL 中使用了一个消息框来检查正在应用的值）。回到 C# 程序 'results[0]' 似乎很好，我可以从中获取值，但是 'results[1]' 给了我一个索引越界错误。我知道这一点，因为如果我省略 '+ (double)results[1]' 我不会收到任何错误。此外，如果我不在 DLL 中尝试修改“test[1]”，它会保留来自 C# 的原始值（在我的示例 0.0 中）。
Obviously I am not doing something right but this is the closest I have been able to get to having it work at all. Everything else I have tried fails miserably.
显然我没有做正确的事情，但这是我最接近让它工作的。我尝试过的其他一切都失败了。
Any help would be greatly appreciated.
任何帮助将不胜感激。
回答by Srikar Doddi
I am not sure what is going wrong, but I can certainly point you to an article that talks about p/invoke. see if this helps you.
我不确定出了什么问题，但我当然可以为您指出一篇关于 p/invoke 的文章。看看这是否对你有帮助。
回答by Dаn
I'm guessing you already know C++; if that's the case, you really should look at C++/CLI which lets you easily use managed code (.NET) from C++. The code you've shown above really isn't very C#-like (you should completely avoid unsafe).
我猜你已经知道 C++；如果是这种情况，您真的应该看看 C++/CLI，它可以让您轻松使用 C++ 中的托管代码 (.NET)。您上面显示的代码确实不是很像 C#（您应该完全避免unsafe）。
回答by JP Alioto
Similar question on SO here. Your looking at an opaque pointer, so it's likely a by-ref system InPtr as described in the other thread.
SO here上的类似问题。您正在查看一个不透明的指针，因此它可能是另一个线程中描述的 by-ref 系统 InPtr。
By the way, why not make it a double* instead of double**. That would make life easier, I think.
顺便说一句，为什么不把它变成双*而不是双**。我想，那会让生活更轻松。
回答by Simon Broadhead
There's no need for unsafe code. In fact, there's no need to pass by reference at all. If your signature looks like this:
不需要不安全的代码。事实上，根本不需要通过引用传递。如果您的签名如下所示：
void test_function (double *test)
and your import looks like this:
您的导入如下所示：
static extern void test_function(double[] Result);
Then everything should work fine. That is, assuming you only need to modify the array and not return a completely new array.
然后一切正常。也就是说，假设您只需要修改数组而不返回一个全新的数组。
