How to pass structure as pointer in C dll from C#

Question

I am working on simple telephony application where I am changing the class of service of panasonic pbx extension. For that I am using "Tapi32.dll" which has methods in c++. Now as per my need I have to pass two argument both integer pointer type. One Argument is getting passed correctly but I am not able to pass second argumnet which is structure type.

Here is my code...

[DllImport("Tapi32.dll", CharSet=CharSet.Auto, SetLastError=true)]
unsafe private static extern int lineDevSpecific(int* hLine, int* lpParams);

[StructLayout(LayoutKind.Sequential)]
public struct UserRec {
    [MarshalAs(UnmanagedType.I4)]
    public int dwMode=4;
    public int dwParam1=8;
}

unsafe static void Main(string[] args) {
    int vline=int.Parse("Ext101");
    int* hline = &vline;
    lineDevSpecific(hline, ref UserRec userrec);
}

stackoverflow.com/questions/4558082/…

user1968030
– user1968030

2013-03-04 08:16:39 +00:00
Commented Mar 4, 2013 at 8:16 — user1968030
– user1968030, Commented Mar 4, 2013 at 8:16

Community · Accepted Answer · 2017-05-23 11:50:34Z

2

[DllImport("Tapi32.dll", SetLastError=true)]
unsafe private static extern int lineDevSpecific(int* hLine, IntPtr lpParams);

unsafe static void Main(string[] args) {
    int vline=int.Parse("Ext101");
    int* hline=&vline;

    var sizeUserRec=Marshal.SizeOf(typeof(UserRec));
    var userRec=Marshal.AllocHGlobal(sizeUserRec);
    lineDevSpecific(hline, userRec);
    var x=(UserRec)Marshal.PtrToStructure(userRec, typeof(UserRec));
    Marshal.FreeHGlobal(userRec);
}

Take a look of this answer of question

Physical disk size not correct (IoCtlDiskGetDriveGeometry)

You can find some more to make marshalling easier and more reusable.

edited May 23, 2017 at 11:50

CommunityBot

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answered Mar 4, 2013 at 8:30

Ken Kin

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2 Comments

vikas Over a year ago

ken Sir I am getting error "cannot have instance field initializers in structs c#"

Ken Kin Over a year ago

@vikas: You cannot have the field initializers that way. Just remove the default values of dwMode and dwParam1.

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