Load a C-Dll in C# with struct array as parameter

Question

I try to import functions from my C-Dll. A function has a struct array as a parameter. The struct will be filled in the function.

struct test
{
    int test1;
    int test2;
};

void FillStruct( struct test stTest[], int size)
{
    if(size == 2){
        stTest[0].test1 = 5;
        stTest[0].test2 = 5;

        stTest[1].test1 = 2;
        stTest[1].test2 = 2;
    }
}

The method FillStruct should be used in C#.

I think I have to create the struct in C#. Must I marshal the struct if I use memcpy in the Fillstruct?

Just declare your own version of it, there's nothing complicated about a struct with two int members. The pinvoke marshaller takes care of marshaling the array and its elements. Nothing complicated either, it simply pins the array and passes a pointer to the first element. Writing C code that just doesn't do anything when the wrong argument is passed is a bad idea, return an error code. — Hans Passant
– Hans Passant, Commented May 30, 2015 at 20:31
Thanks a lot, i tried tu abstract the problem. In FillStruct i use memcpy. I hope this runs without any problems. — lalelu
– lalelu, Commented May 30, 2015 at 20:36
Well, never post fake code. Using memcpy() is fine, as long as you don't ignore size. — Hans Passant
– Hans Passant, Commented May 30, 2015 at 20:38

Zotta · Accepted Answer · 2015-05-30 20:55:18Z

2

struct Test
{
    public int test1;
    public int test2;
}

[DllImport("mydll", CallingConvention = Cdecl)]
public static extern void FillStruct( Test[] stTest, int size);

[...]
var test = new Test[n];
FillStruct(test, test.Length);

I don't see the problem here. It does not matter what you do with the memory in your c code: as long as you don't cause buffer overflows, you can read, write an copy all you want. c# arrays are just the type and length of the array, followed by the data. When you use p/invoke with simple structs, a pointer to the first element in the original array will be passed to your c code.

edited May 30, 2015 at 20:55

answered May 30, 2015 at 20:46

Zotta

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