How to export unmanaged dll (for custom types)?

Ken H

12y2k

hello,

My code is this:

#include

typedef struct CalTest{

int x;

int y;

}OurType;

extern "C"{

_declspec(dllexport) OurType MyFun(int a,int 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.

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes12y ago
Accepted 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.dll",CallingConvention = 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);
}
}
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Ken H12y ago
Great! The problem is resolved.

Thank for you,Vulpes. :)
0
Ken H12y ago
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 a,char *b){
OurType ot;

ot.Age=a;
ot.Name=b;

return ot;
}
}

C Sharp codes:
[StructLayout(LayoutKind.Sequential,Pack=1)]
public struct OurTypeCS {
public int Age;
public string Name;
}

[DllImport("calc88.dll",CallingConvention=CallingConvention.Cdecl)]
public static extern OurTypeCS MyFun(Int32 a,ref 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(age,ref name);
MessageBox.Show(otcs.Age.ToString()+" and "+otcs.Name);

}
catch (Exception err){

MessageBox.Show("Error Information:" + err.ToString());
}


}
0
Vulpes12y ago
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();
}
}

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