Using arrays and pointers in C# with C DLL
Solution 1
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:
void test_function (double *test)
and your import looks like this:
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.
Solution 2
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
).
JaredPar
Developer at Microsoft working on a language and operating system incubation project. Sites VsVim - VsVim on Visual Studio Gallery Blog - http://blog.paranoidcoding.com/ Twitter - http://twitter.com/jaredpar Linked In - http://www.linkedin.com/in/jaredpar Google+ - +JaredParsons Email: [email protected]
Updated on July 06, 2022Comments
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JaredPar about 2 years
I am very new to C# (just started learning in the past week).
I have a custom DLL written in C with the following function:
DLLIMPORT void test_function (double **test)
What I am looking to do is have a pointer from C# for the array '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.
In the C# program I have something similar to:
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:
*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).
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.
Any help would be greatly appreciated.