Function Pointer Interoperabilit y in C# with Native Code

[natarajchakraborty]

Hi All,

I have a serious problem here which is bugging me for past few days.

I have a native DLL(Win32), and it exposes only on function called

GetFunctionList

Now this function takes a pointer to pointer of a Structure as an argument.

The Structure is something like

struct func_pointer_li st{

void (*fnA)(int a,int b);
int (*fnB)(float a, double b);
}

Now I have to write an Wrapper for this Native DLL in C#.

What I did was I wrote an Structure in C# containing some delegates like this....

[UnmanagedFuncti onPointer(Calli ngConvention.Wi napi)]
public delegate void pfnA(int a, int b)

[UnmanagedFuncti onPointer(Calli ngConvention.Wi napi)]
public delegate int pfnA(float a, double b)

[StructLayout(La youtKind.Sequen tial, CharSet = CharSet.Ansi)]
public struct func_pointer_li st
{
public pfnA fnA;
public pfnB fnB;
}


Now I call this Function called GetFunctionList something like this:

using FUNCTION_LIST_P TR_PTR = System.IntPtr;

[DllImport("NATI VE.DLL", CharSet = CharSet.Ansi)]
public extern static void C_GetFunctionLi st(ref FUNCTION_LIST_P TR ppFunctionList) ;

in Code file:

System.IntPtr pp = System.IntPtr.Z ero;
myClass.C_GetFu nctionList(ref pp);
func_pointer_li st fnList = (func_pointer_l ist)Marshal.Ptr ToStructure(pp, typeof(func_poi nter_list));

I get the Exception 'InvalidFuction PointerInDelega te' in the Second line (Marshel) saying
"Invalid function pointer 0x1a201000 was passed into the runtime to be converted to a delegate. Passing in invalid function pointers to be converted to delegates can cause crashes, corruption or data loss."

Do any of you have any clue as to what is the right method of doing this.....
Where am I wrong doing this...
Does the above code not gonna work...

Thanx in Advance

[natarajchakraborty]

Hi All,

I have a serious problem here which is bugging me for past few days.

I have a native DLL(Win32), and it exposes only on function called

GetFunctionList

Now this function takes a pointer to pointer of a Structure as an argument.

The Structure is something like

struct func_pointer_li st{

void (*fnA)(int a,int b);
int (*fnB)(float a, double b);
}

Now I have to write an Wrapper for this Native DLL in C#.

What I did was I wrote an Structure in C# containing some delegates like this....

[UnmanagedFuncti onPointer(Calli ngConvention.Wi napi)]
public delegate void pfnA(int a, int b)

[UnmanagedFuncti onPointer(Calli ngConvention.Wi napi)]
public delegate int pfnA(float a, double b)

[StructLayout(La youtKind.Sequen tial, CharSet = CharSet.Ansi)]
public struct func_pointer_li st
{
public pfnA fnA;
public pfnB fnB;
}


Now I call this Function called GetFunctionList something like this:

using FUNCTION_LIST_P TR_PTR = System.IntPtr;

[DllImport("NATI VE.DLL", CharSet = CharSet.Ansi)]
public extern static void C_GetFunctionLi st(ref FUNCTION_LIST_P TR ppFunctionList) ;

in Code file:

System.IntPtr pp = System.IntPtr.Z ero;
myClass.C_GetFu nctionList(ref pp);
func_pointer_li st fnList = (func_pointer_l ist)Marshal.Ptr ToStructure(pp, typeof(func_poi nter_list));

I get the Exception 'InvalidFuction PointerInDelega te' in the Second line (Marshel) saying
"Invalid function pointer 0x1a201000 was passed into the runtime to be converted to a delegate. Passing in invalid function pointers to be converted to delegates can cause crashes, corruption or data loss."

Do any of you have any clue as to what is the right method of doing this.....
Where am I wrong doing this...
Does the above code not gonna work...

Thanx in Advance

The problem is solved.... as of now...

What I did was just added some more Tags in the member function Defination of the structure and also added the Pack Tag in the Structure Layout... something like this:

[UnmanagedFuncti onPointer(Calli ngConvention.Wi napi)]
public delegate void pfnA(int a, int b)

[UnmanagedFuncti onPointer(Calli ngConvention.Wi napi)]
public delegate int pfnA(float a, double b)

[StructLayout(La youtKind.Sequen tial, CharSet = CharSet.Ansi , Pack=2)]
public struct func_pointer_li st
{

[MarshalAs(Unman agedType.Functi onPtr)]
public pfnA fnA;

[MarshalAs(Unman agedType.Functi onPtr)]
public pfnB fnB;
}

Possibly the problem was due to the Pack specification.. .
The rest of the Code Stands Same.... and it Worked...

Although I am stuck in some other problem, probably not a C# problem but a Domain Problem....

Anyways Thanx for the Notice...

And

Cheers