How to export unmanaged dll (for custom types)?

Question

hello My code is this: #include typedef struct CalTest{ int x; int y; }OurType; extern C{ _declspec(dllexport) OurType MyFun(int aint b){ OurType ot; /* Do some processing. */ ot.x=a; // Assumed to be a ot.y=b; // Assumed to be b return ts; } } In addition What types can accept its(OurType)in c#? Thanks.

Vulpes · Answer

As soon as you introduce strings Platform Invoke (DllImport) starts to get difficult! When you have a char* argument in a function or a char* field in a struct it's best to use IntPtr from the C# side and then marshal your strings to and from the pointer: [StructLayout(LayoutKind.Sequential)] public struct OurTypeCS { public int Age; private IntPtr _name; public string Name { get { return Marshal.PtrToStringAnsi(_name); } } } [DllImport(calc88.dllCallingConvention = CallingConvention.Cdecl)] public static extern OurTypeCS MyFun(Int32 a IntPtr b); private void button1_Click(object sender EventArgs e){ int age = Convert.ToInt32(textBox1.Text); string name = Convert.ToString(textBox2.Text); IntPtr s = Marshal.StringToHGlobalAnsi(name); try{ OurTypeCS otcs; otcs = MyFun(age s); MessageBox.Show(otcs.Age.ToString()+  and  +otcs.Name); } catch (Exception err){ MessageBox.Show(Error Information: + err.ToString()); } finally{ Marshal.FreeHGlobal(s); } }

Ken H · Answer

Great! The problem is resolved. Thank for youVulpes. :)

Ken H · Answer

System Tip: type signature method is incompatible with PInvoke. Dll source codes: #include typedef struct CalTest{ int Age; char *Name; }OurType; extern C{ _declspec(dllexport)OurType MyFun(int achar *b){ OurType ot; ot.Age=a; ot.Name=b; return ot; } } C Sharp codes: [StructLayout(LayoutKind.SequentialPack=1)] public struct OurTypeCS { public int Age; public string Name; } [DllImport(calc88.dllCallingConvention=CallingConvention.Cdecl)] public static extern OurTypeCS MyFun(Int32 aref string b); private void button1_Click(object sender EventArgs e){ int age = Convert.ToInt32(textBox1.Text); string name = Convert.ToString(textBox2.Text); try{ OurTypeCS otcs; otcs=MyFun(ageref name); MessageBox.Show(otcs.Age.ToString()+ and +otcs.Name); } catch (Exception err){ MessageBox.Show(Error Information: + err.ToString()); } }

Vulpes · Answer

If you're wanting to use that function in a C# application then: 1. You'll need to import it using the DllImport attribute. 2. You'll need to mimic the struct OurType from C# code. Here's some code. I've assumed the dll is called calltest.dll and has been copied to the C# executable's directory: using System; using System.Runtime.InteropServices; [StructLayout(LayoutKind.Sequential)] struct OurType { public int x; public int y; } class Test { [DllImport(calltest.dll)] static extern OurType MyFun(int a int b); static void Main() { OurType our = MyFun(1 2); Console.WriteLine(x = {0} y = {1} our.x our.y); Console.ReadKey(); } }