How to marshal a struct

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Thomas - 23 Jul 2004 23:01 GMT

Hi,

I am having difficulty accesing the member data in a struct.

This what I am doing.

In unmanaged code
typedef struct {
char name[20];
int id;
} person;

In C#

[StructLayout(LayoutKind.Sequential)]
public class person
{
[UnmanagedType.ByValTStr, SizeConst=20)]
public string name;
public int id;
}

[DllImport("TestDLL.dll")]
public static extern void SetStructData(
[MarshalAs(UnmanagedType.LPStruct)]
person pp );

When I pass the struct to unmanaged code, the data is all junk.

Can someone tell me what I am doing wrong.

Thanks.

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Suresh - 23 Jul 2004 23:09 GMT

Specify the character set and try

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]
public struct person
{
[UnmanagedType.ByValTStr, SizeConst=20)]
public string name;
public int id;
}

> Hi,
>
[quoted text clipped - 28 lines]
>
> Thanks.

Reply to this Message

BMermuys - 24 Jul 2004 02:00 GMT

Hi,

> Hi,
>
[quoted text clipped - 17 lines]
> public int id;
> }

Using struct:
---

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Ansi)]
public struct person
{
[UnmanagedType.ByValTStr, SizeConst=20)]
public string name;
public int id;
}

[DllImport("TestDLL.dll")]
public static extern void SetStructData( ref person pp ); // you can see
changes made to struct

Using class:
---

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Ansi)]
public class person
{
[UnmanagedType.ByValTStr, SizeConst=20)]
public string name;
public int id;
}

[DllImport("TestDLL.dll")]
public static extern void SetStructData( [In,Out] person pp ); // here
[In,Out] is required if you want to see changes!

HTH,
greetings

> When I pass the struct to unmanaged code, the data is all junk.
>
> Can someone tell me what I am doing wrong.
>
> Thanks.

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Thomas - 26 Jul 2004 11:24 GMT

Thanks for your reply.

It did not work. I just cannot figure out why char[] is all junk data.

> Hi,
>
[quoted text clipped - 58 lines]
> >
> > Thanks.

Reply to this Message

BMermuys - 26 Jul 2004 12:25 GMT

> Thanks for your reply.

> > > [StructLayout(LayoutKind.Sequential)]
> > > public class person
[quoted text clipped - 3 lines]
> > > public int id;
> > > }

> It did not work. I just cannot figure out why char[] is all junk data.

The marshalling of such a simple struct itself is no problem, I use it all
the time.
Something else must be wrong, maybe you're translating the wrong struct or
the function isn't working properly.

HTH,
greetings

> > Hi,
> >
[quoted text clipped - 58 lines]
> > >
> > > Thanks.

Reply to this Message

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How to marshal a struct

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