[Mono-devel-list] Calling Native C api - Marshalling issue.

2005-07-28 Thread Yogendra Thakur 
 
I am getting problem while executing the c library function from C#.

Following is the equivalent code .

C Code :
--- 
 //This is the structure in C
 typedef struct MyDataType
 {
   u_intdata1;
u_int   data2;
 } MyData;

//This is the C function which is called by passing pointer to above
structure
 function u_int DoSomeOperation(MyData* pData)
 {
  return pData-data1 +pData-data2;
 }


 C# Code  :

Following code shows how I am executing that call.

 using System;
 using System.Runtime.InteropServices;
 namespace Test
 {
  //Define equivalent class to MyData structure
  [StructLayout(LayoutKind.Sequential)]
  public class CSMyData
  {
   public UInt32 data1;
   public UInt32 data2;
  }



  public class Test
  {

   //Import the dll and define C function.
   [DllImport (mylibrary.dll, EntryPoint=DoSomeOperation)]
   static extern Int32 OperateData( ref  CSMyData pData);
   //Other way of defining
   //static extern Int32 OperateData( [In,Out]  CSMyData pData);

   //main function for console application
   static void Main()
   {
UInt32 result = 0;
CSMyData inData = new CSMyData();

inData.data1 = 0x;
inData.data2 = 0xFF;

result = OperateData(ref inData);

Console.WriteLine( Addition =  result.ToString();
   }

  }

}


Issue:

When I am printing value in the  C code side ,ie  in DoSomeOperation
function , the values are corrupted.

Please let me know what part is wrong.

regards,
Yogi
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Re: [Mono-devel-list] Calling Native C api - Marshalling issue.

2005-07-28 Thread Zoltan Varga 
  Hi,

  classes are by default passed by-ref to unmanaged code, i.e. a pointer to the
data is passed to the C side. If you define your managed method as 'ref', then
the unmanaged code will receive a pointer-to-a-pointer to the data. Try
removing the 'ref', or defining CSMyData as a struct, which by default
marshalled
by-value.

 Zoltan


On 7/28/05, Yogendra Thakur [EMAIL PROTECTED] wrote:
 
 I am getting problem while executing the c library function from C#.
 
 Following is the equivalent code .
 
 C Code :
 ---
  //This is the structure in C
  typedef struct MyDataType
  {
u_intdata1;
 u_int   data2;
  } MyData;
 
 //This is the C function which is called by passing pointer to above
 structure
  function u_int DoSomeOperation(MyData* pData)
  {
   return pData-data1 +pData-data2;
  }
 
 
  C# Code  :
 
 Following code shows how I am executing that call.
 
  using System;
  using System.Runtime.InteropServices;
  namespace Test
  {
   //Define equivalent class to MyData structure
   [StructLayout(LayoutKind.Sequential)]
   public class CSMyData
   {
public UInt32 data1;
public UInt32 data2;
   }
 
 
 
   public class Test
   {
 
//Import the dll and define C function.
[DllImport (mylibrary.dll, EntryPoint=DoSomeOperation)]
static extern Int32 OperateData( ref  CSMyData pData);
//Other way of defining
//static extern Int32 OperateData( [In,Out]  CSMyData pData);
 
//main function for console application
static void Main()
{
 UInt32 result = 0;
 CSMyData inData = new CSMyData();
 
 inData.data1 = 0x;
 inData.data2 = 0xFF;
 
 result = OperateData(ref inData);
 
 Console.WriteLine( Addition =  result.ToString();
}
 
   }
 
 }
 
 
 Issue:
 
 When I am printing value in the  C code side ,ie  in DoSomeOperation
 function , the values are corrupted.
 
 Please let me know what part is wrong.
 
 regards,
 Yogi
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RE: [Mono-devel-list] Calling Native C api - Marshalling issue.

2005-07-28 Thread Yogendra Thakur 
Thanks Massi  Zoltan.

It works after removing the ref. As Zoltan said, by defualt classed are
passed as reference to unmanaged code.

-YoGi 

-Original Message-
From: Massimiliano Mantione
To: Yogendra Thakur
Cc: 'mono-devel-list@lists.ximian.com '
Sent: 7/28/05 11:17 AM
Subject: Re: [Mono-devel-list] Calling Native C api - Marshalling issue.


On Thu, 2005-07-28 at 10:15 -0400, Yogendra Thakur wrote:
  I am getting problem while executing the c library function from C#.
   //Define equivalent class to MyData structure
   [StructLayout(LayoutKind.Sequential)]
   public class CSMyData
   {

either should be a struct, not a class...

//Import the dll and define C function.
[DllImport (mylibrary.dll, EntryPoint=DoSomeOperation)]
static extern Int32 OperateData( ref  CSMyData pData);
//Other way of defining
//static extern Int32 OperateData( [In,Out]  CSMyData pData);

...or you should omit the ref (or the [In,Out]).

With these modification it works.

The issue is that if CSMyData is a struct, then the ref (or the
[In,Out]) is needed to get the address of the struct.
But if CSMyData is a class, marshalling converts it correctly.
I am no marshalling expert, but I think that if you put the ref
you pass the address of the object reference :-)

Ciao,
  Massi

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