Re: ZeroMemory - C# Discussion Boards

3-Sep-02 2:06

Hello, its me again [ Eek! | :eek:

run while you can] Big Grin | :-D

is there a function similar to ZeroMemory i can use?

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

Rodney S. Foley3-Sep-02 2:13

Rodney S. Foley

3-Sep-02 2:13

There is no equivelent method to the Windows ZeroMemory function in C#. You need to remember that the memory in C# is managed for you. What are you trying to do, maybe I can help you find a solution.

Aalst

Nnamdi Onyeyiri3-Sep-02 7:46

3-Sep-02 7:46

i was trying to convert this[^], and found that it was giving an exception that an instance of an object is not bla bla bla, but i HAVE initisated it Confused | :confused:

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leppie3-Sep-02 2:28

3-Sep-02 2:28

byte buffer = new byte[size]; 
IntPtr ptr = Marshal.AllocHGlobal(size * Marshal.SizeOf(typeof(byte)));
Marshal.Copy(buffer, 0, ptr, size);

I dunno if this will provide the same ?

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Nnamdi Onyeyiri3-Sep-02 7:48

3-Sep-02 7:48

i was converting http://www.codeguru.com/system/cdr.html[^] and foundthat it didnt work, it said that my MCI_OPEN_PARMS variable, was referencing an object that doesnt exist, when it was. the only bit of the C++ code i didnt convert was the ZeroMemory bit, so i presumed that may be the problem.

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Nnamdi Onyeyiri3-Sep-02 8:02

3-Sep-02 8:02

i have discovered that when i changed the second parameter of mciSendCommand from MCI_OPEN to 0, it did not give the error, but nothing happened.

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leppie3-Sep-02 9:51

3-Sep-02 9:51

Nnamdi Onyeyiri wrote:
i have discovered that when i changed the second parameter of mciSendCommand from MCI_OPEN to 0, it did not give the error, but nothing happened.

MCI_OPEN = 0x0803;

MCI_OPEN_PARMS is a struct. What does the 2 have to do with each other?

I will have a look. Smile | :)

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Nnamdi Onyeyiri3-Sep-02 9:55

3-Sep-02 9:55

leppie wrote:
MCI_OPEN = 0x0803;

i know that, im passing the value as 0x0803.

leppie wrote:
MCI_OPEN_PARMS is a struct. What does the 2 have to do with each other?

according to the article i gave the link for in my original post, it uses mciSendCommand(0, MCI_OPEN, flags, MyOpenParms);

but when i do this, i get the exception.

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CDR solution

leppie3-Sep-02 10:34

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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Re: CDR solution

leppie3-Sep-02 22:56

3-Sep-02 22:56

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Rüpel3-Sep-02 2:48

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

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

access memory within unmanaged dll

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