Re: Help please with pointers to callbacks in structs
Brian
Date: 04/08/04
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Date: Thu, 08 Apr 2004 00:59:18 -0000
Thank you so much! I REALLY appreciate your taking the time to step me
through this!
I'll give it a try and see what happens.
Brian
BMermuys <someone@someone.com> wrote:
> Hi,
> see inline;
> <Brian> wrote in message news:1078e5bgehc4q20@corp.supernews.com...
>> I am very new to C# programming and have run into a problem.
>>
>> I apologize for the repost of this article. For some reason, my news
>> reader attached it to an existing thread.
>>
>> First off, I have an SDK that I have written for C/C++ and would like to
>> port it to C# if at all possible.
>>
>> Basically, I've got a structure that I need to pass to the C-style DLL
>> (i.e. no mangled names - everything is __stdcall). This structure needs
>> to contain pointers to callback functions that the DLL can use to notify
>> the C# application when certain events occur. In addition, I need to use
>> SetEnvironmentVariable and pass a string containing a pointer to a
>> character array for special processing by the DLL. I've included some
>> code that shows basically everything I'm looking to do.
>>
>> To save time, I understand how to get access to exported functions within
>> DLLs.
>>
>>
>> // this structure will be filled by the DLL and will be passed
>> // to the callback for function2, (i.e. FnPtr2's typedef)
>>
>> typedef struct _toPassAsArgumentStruct
>> {
>> int a;
>> int b;
>> double c;
>> } TO_PASS_AS_ARGUMENT;
> In c#:
> [StructLayout(StructLayout.Sequential)]
> public struct PassAsArgStruct
> {
> public int a;
> public int b;
> public double c;
> }
>>
>>
>> // these are the typedef's for two callback functions that will be
>> // stored in the structure, DEMOSTRUCT
>>
>> typedef BOOL (__stdcall *FnPtr1)(DWORD i, char *path, DWORD pathLength);
>> typedef BOOL (__stdcall *FnPtr2)(TO_PASS_AS_ARGUMENT *structure);
> Declare a delegate for each callback:
> public delegate bool DelFn1(uint i, IntPtr pPath, uint pathLength);
> public delegate bool DelFn2(ref ToPassAsArgStruct structure);
>>
>>
>> typedef struct _demoStruct
>> {
>> FnPtr1 function1;
>> FnPtr2 function2;
>> } DEMOSTRUCT;
> In c#: (use the delegates)
> [StructLayout(StructLayout.Sequential)]
> public struct DemoStruct
> {
> public DelFn1 function1;
> public DelFn2 function2;
> }
>>
>> // MyFunction1 and MyFunction2 are called by the DLL
>>
>> BOOL MyFunction1(DWORD i, char *path, DWORD pathLength)
>> {
>> strcpy(path, "unknown");
>> return TRUE;
>> }
> [DllImport("kernel32.dll",CharSet=CharSet.Ansi)]
> public static extern long lstrcpyA (IntPtr pDst, string sSrc);
> private bool MyFunction1(uint i, IntPtr pPath, uint pathLength)
> {
> // TODO check pathLength before writing
> lstrcpyA (pPath, "unknown");
> return true;
> }
>>
>> BOOL MyFunction2(TO_PASS_AS_ARGUMENT *structure)
>> {
>> structure->a = 5;
>> return TRUE;
>> }
>>
> In c#:
> private bool MyFunction2(ref ToPassAsArgStruct s)
> {
> s.a = 5;
> return true;
> }
>> char global_text[5] = {"test"};
>>
>> // simple_function is called by the non-DLL (i.e. the application)
>>
>> void simple_function()
>> {
>> char text[128] = {0};
>>
>> DEMOSTRUCT ds = {0};
>>
>> // Are these four statements possible in C#?
>>
>> ds.function1 = MyFunction1;
>> ds.function2 = MyFunction2;
>>
>> // the contents of 'text' will be passed to the DLL.
>> sprintf(text, "%x", &global_text);
>>
>> SetEnvironmentVariable("test", text);
> [DllImport("kernel32.dll",CharSet=CharSet.Auto)]
> public static extern bool SetEnvironmentVariable (string sName, string
> sValue);
> private DemoStruct ds;
> private IntPtr pGlobalText = IntPtr.Zero;
> void SimpleFunction()
> {
> ds = new DemoStruct();
> ds.function1 = new DelFn1( MyFunction1 );
> ds.function2 = new DelFn2( MyFunction2 );
> // Allocate unmanaged memory the dll can read/write
> pGlobalText = Marshal.AllocHGlobal (5);
> lstrcpyA ( pGlobalText, "test" ); // write
> // pass pointer as hex string value
> SetEnvironmentVariable("test", pGlobalText.ToInt32().ToString("X") );
> }
> * After this function you can :
> - read from globaltext
> Console.WriteLine ( Marshal.PtrToStringAnsi( pGlobalText ) ); /// READ
> - write to globaltext
> lstrcpyA ( pGlobalText, text );
> - cleanup globaltext
> (only if dll doesn't need globaltext anymore)
> Marshal.FreeHGlobal( pGlobalText );
> HTH,
> greetings
>>
>>
>> }
>> --
>>
>> TIA,
>> Brian
>>
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