access memory within unmanaged dll - C# Discussion Boards

3-Sep-02 10:34

Hi , it was a bit trickey, but using int's did the job Smile | :)

[DllImport("winmm.dll" , CharSet = CharSet.Ansi)]
static extern int mciSendCommand(int device, int msg, int flags, int param);

const int MCI_OPEN = 0x0803;
const int MCI_DEVTYPE_CD_AUDIO = 516;
const int MCI_SET                         = 0x080D;
const int MCI_SET_DOOR_OPEN              = 0x00000100;
const int MCI_SET_DOOR_CLOSED            = 0x00000200;

[StructLayout(LayoutKind.Sequential)]
public class MCI_OPEN_PARMS
{
	public int    dwCallback; 
	public int  wDeviceID;
	public int       lpstrDeviceType;
	public int       lpstrElementName; 
	public int       lpstrAlias; 
}

[Flags]
public enum MCIOPEN
{
	SHAREABLE             = 0x00000100,
	ELEMENT               = 0x00000200,
	ALIAS                 = 0x00000400,
	ELEMENT_ID            = 0x00000800,
	TYPE_ID               = 0x00001000,
	TYPE                  = 0x00002000,
}

and the implementation Smile | :)

MCIOPEN flags;

flags = MCIOPEN.TYPE | MCIOPEN.TYPE_ID | MCIOPEN.SHAREABLE;

MCI_OPEN_PARMS param = new MCI_OPEN_PARMS();
IntPtr ptr = Marshal.AllocHGlobal(Marshal.SizeOf(param));
param.lpstrDeviceType = MCI_DEVTYPE_CD_AUDIO;

Marshal.StructureToPtr(param, ptr,  true);
int result = mciSendCommand(0, MCI_OPEN, (int) flags, ptr.ToInt32()); //get the ID
Marshal.PtrToStructure(ptr, param);
Marshal.FreeHGlobal(ptr);

result = mciSendCommand(param.wDeviceID, MCI_SET, MCI_SET_DOOR_OPEN, 0); //open drive
result = mciSendCommand(param.wDeviceID, MCI_SET, MCI_SET_DOOR_CLOSED, 0); //close drive

OK, I didnt bother with drive numbers Blush | :O

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Re: CDR solution

Nnamdi Onyeyiri3-Sep-02 21:54

3-Sep-02 21:54

thanks a lot leppie. you appear to be very persistant in helping me, thankyou Big Grin | :-D

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"All programmers are playwrights and all computers are lousy actors."

Re: CDR solution

leppie3-Sep-02 22:56

3-Sep-02 22:56

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Re: ZeroMemory

Rüpel3-Sep-02 2:48

access memory within unmanaged dll

3-Sep-02 2:48

i know this doesn't apply if some values of your array were already changed, but the runtime asures you, that after constructing everything is set to zero.

thus

byte [] b = new byte[20];
for (int i=0; i<20; ++i)
  if (b[i]!=0) MessageBox.Show("you will not see me");

runs without popping up that window.

:wq

Re: ZeroMemory

Paul Riley3-Sep-02 3:32

Paul Riley

3-Sep-02 3:32

And on top of all the other responses, it should be pointed out that you can always reinitialise any array with the Initialize method.

For example:

byte[] array = new byte[20];
// array is currently all zeros
for (int i=0;i<20;i++)
    array[i] = i;
// array is no longer all zeros
array.Initialize();
// array is all zeros again

string[] array = new string[20];
// array is currently all empty strings
for (int i=0;i<20;i++)
    array[i] = i.ToString();
// array is no longer all empty strings
array.Initialize();
// array is all empty strings again

One of these answers should help now Smile | :)

Paul

Re: ZeroMemory

Nick Parker4-Sep-02 9:12

Nick Parker

4-Sep-02 9:12

You should be able to make an "unsafe" call once you import it, something like this:

[System.Runtime.InteropServices.DllImport("kernel32.dll")]
       unsafe public static extern void ZeroMemory(System.IntPtr ptr ,uint size);

HTH

Nick Parker

Rüpel2-Sep-02 23:45

2-Sep-02 23:45

hi, i'm stuck.
Frown | :(

i'm currently trying to work with an old dll and marshalling and stuff went really fine until now. there's a function in that dll declared like

int foo(void *ppMessage);

the function will do some nasty stuff, allocate local memory for the result and write the pointer to the result in the parameter. (thats why there are two ps in the name)

in c++ it would be something like

byte *result;
foo(&result);
(*result)[0] //is the first byte of the result

i have no idea, how to actually read the result using c# - does anyone know? looks somewhat unmanaged Unsure | :~

thx in advance

:wq

Rüpel2-Sep-02 23:55

2-Sep-02 23:55

ah. just found the Marshal-class - maybe this helps me... Smile | :)

:wq

Stephane Rodriguez.3-Sep-02 0:06

Stephane Rodriguez.

3-Sep-02 0:06

First of all, are you sure about the signature of your C method ?
Isn't it more like this :

int foo(void **ppMessage);

To expose this C function to managed code, you need to declare it as :

[DllImport("user32.dll", CharSet=CharSet.Auto, CallingConvention=CallingConvention.Cdecl)]
public static extern int foo(out IntPtr ppMessage);

where user32.dll must be replaced with the actual DLL name.

And I swallow a small raisin.

Rüpel3-Sep-02 0:38

3-Sep-02 0:38

erm no, i looked it up in the header-file and there's only one star. i'm a bit confused too, but it seems you have to know, that you get a pointer in the specified location.

actually i have solved the thing like this:

[DllImport("theold.dll")]
public static extern Int32 foo(IntPtr [] messagePtr);

...

IntPtr [] messagePtr = new IntPtr[1];
Int32 ret = foo(messagePtr);
Int16 size = Marshal.ReadInt16(messagePtr[0]);
byte [] message = new byte[size];
Marshal.Copy(messagePtr[0],message,0,size);

i know (from the specification) that the first 2 bytes contain the size of the result in bytes.

:wq

leppie3-Sep-02 1:42

3-Sep-02 1:42

Hi, it seems you should be able to remove the array like:

[DllImport("theold.dll")]public static extern Int32 foo(out IntPtr messagePtr);
...
IntPtr messagePtr;
Int32 ret = foo(messagePtr);
Int16 size = Marshal.ReadInt16(messagePtr);
byte [] message = new byte[size];
Marshal.Copy(messagePtr,message,2,size); //remmeber that is only the size, and it is not included in byte[]

I'm interested, does this work too?

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Rüpel3-Sep-02 2:39

3-Sep-02 2:39

1. yep. out works indeed. good idea. but in the foo-call is to be inserted uswell.
2. no, the copy-call was ok, since the size-field is included (i.e. the value is at least 2 for the 2 size-bytes)

finally:

[DllImport("theold.dll")]
public static extern Int32 foo(out IntPtr messagePtr);
...
IntPtr messagePtr;
Int32 ret = foo(out messagePtr);
Int16 size = Marshal.ReadInt16(messagePtr);
byte [] message = new byte[size];
Marshal.Copy(messagePtr,message,0,size);

thx again for your help an ideas Rose | [Rose]

:wq

leppie3-Sep-02 3:27

Re: How can be only one ?

3-Sep-02 3:27

Rüpel wrote:
but in the foo-call is to be inserted uswell.

oops Smile | :)

, happens when u write the code out of your head straight into the textbox Smile | :)

Rüpel wrote:
2. no, the copy-call was ok, since the size-field is included (i.e. the value is at least 2 for the 2 size-bytes)

But wont the fist 2 byte values (being a size value) affect the byte[]?

(oops another typo Smile | :)

, meant to do this)

byte [] message = new byte[size - 2];
Marshal.Copy(messagePtr,message,2,size);

byte [] message = new byte[size - 2];
Marshal.Copy(new IntPtr(messagePtr.ToInt32() + Marshal.SizeOf(typeof(byte))*2),message,0,size - 2);

I'm just interested Smile | :)

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Doing programs

suresh_sathya2-Sep-02 23:39

suresh_sathya

2-Sep-02 23:39

I want to know wheather we can write components using c# in place of ATL COM.i.e..is it possible to write everything whatever we do in ATLCom.

Re: Doing programs

Stephane Rodriguez.2-Sep-02 23:54

Stephane Rodriguez.

2-Sep-02 23:54

It depends if you intend to consume these components from unmanaged or managed code.

If that's managed code, then you are talking about the whole .NEt platform. A C# user control exposes interfaces that can be used in a VB.Net class.

If that's unmanaged code :
You'd better have good reasons to do so. ATL/COM components do not require the .Net framework to work.

And yes, there are tutorials about this in MSDN. You usually end up by doing a tlbexp.exe or regasm.exe (which is the opposite of importing a COM type-library).

And I swallow a small raisin.

How can be only one ?

candan2-Sep-02 16:42

candan

2-Sep-02 16:42

If I want my AP be only one ? How can I do this in C#? Confused | :confused:

There is an example in VC http://www.codeproject.com/threads/singleinstance.asp

Stephane Rodriguez.3-Sep-02 0:11

Stephane Rodriguez.

3-Sep-02 0:11

VC apps usually take advantage of mutexes. Go in the .Net framework MSDN doc, search "Mutex". Finish the implementation. Big Grin | :-D

And I swallow a small raisin.

Re: How can be only one ?

Christian Graus3-Sep-02 0:46

Christian Graus

3-Sep-02 0:46

When I saw this, I immediately thought of 'Highlander'.....

Christian

We're just observing the seasonal migration from VB to VC. Most of these birds will be killed by predators or will die of hunger. Only the best will survive - Tomasz Sowinski 29-07-2002 ( on the number of newbie posters in the VC forum )

Cats, and most other animals apart from mad cows can write fully functional vb code. - Simon Walton - 6-Aug-2002

Re: How can be only one ?

Richard Deeming3-Sep-02 1:00

Richard Deeming

3-Sep-02 1:00

This should do it:
http://msdn.microsoft.com/library/en-us/dndotnet/html/reaworapps1.asp[^]

Passing null

Nnamdi Onyeyiri2-Sep-02 8:09

2-Sep-02 8:09

I am using the ChangeDisplaySettings function from user32.dll, but when i need to reset to the default regitry settings, msdn says do ChangeDisplaySettings(null, 0); but it doesnt like the null value Frown | :(

what should i do?

Suspicious | :suss: Email: theeclypse@hotmail.com URL: http://www.onyeyiri.co.uk
"All programmers are playwrights and all computers are lousy actors."

Paul Riley2-Sep-02 8:17

Paul Riley

2-Sep-02 8:17

What do you mean by "doesn't like"?

Paul

Nnamdi Onyeyiri2-Sep-02 8:25

2-Sep-02 8:25

it does not compile, as the function definition is as follows.

ChangeDisplaySettings(ref DEVMODE d, int flags);

Suspicious | :suss: Email: theeclypse@hotmail.com URL: http://www.onyeyiri.co.uk
"All programmers are playwrights and all computers are lousy actors."

leppie2-Sep-02 9:17

2-Sep-02 9:17

DEVMODE is a struct.

1. just make another definition

ChangeDisplaySettings(object dummy, int flags);

or

2. change DEVMODE to a class with a sequential layout. Then you can pass null.

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Nnamdi Onyeyiri2-Sep-02 9:23