Re: access memory within unmanaged dll - C# Discussion Boards

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);

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"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

2-Sep-02 9:23

i have done the second one, but the app doesnt run now, wen you try and run it, it doesnt, nt even listed in the Process List. Confused | :confused:

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

leppie2-Sep-02 12:11

2-Sep-02 12:11

I sent you VS solution, that happened to me too, seemed to be due not changing the enum declaration from ref DEVMODE to just DEVMODE ,its a class now so we dont need to. I however had to add the OutAttribute the the declaration.

Smile | :)

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Rickard Andersson²⁰2-Sep-02 10:45

Rickard Andersson²⁰

2-Sep-02 10:45

How about making the function unsafe?
Then use a pointer as parameter.
But that's maybe not possible when it's an imported function!?

Rickard Andersson@Suza Computing
C# and C++ programmer from SWEDEN!
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Display Mode

Nnamdi Onyeyiri2-Sep-02 2:22

2-Sep-02 2:22

have geen trying to get he current displaymode but have been unable, my latest attmpt was to try[^] and convert this articles code, but i had a little difficulty. I found the content of the DEVMODE struct on MSDN and put it into my code. I declare the EnumDisplaySettings like this

[DllImport("User32.dll")]<br />
public static extern bool EnumDisplaySettings(string lpszDeviceName, int iModeNum, DEVMODE lpDevMode);

then use it in code like this:

DEVMODE dm = new DEVMODE();
EnumDisplaySettings(null, -1, dm);

but i get the exception 'object reference not set to an instance of an object' yet clearly, a DEVMODE object has been initiated. Confused | :confused:

any help would be appreciated.

*sudden thought* in the decleration of the DEVMODE struct, on MSDN, a couple of the members where of tpye TCHAR, declared like this.

TCHAR  dmDeviceName[CCHDEVICENAME];<br />
TCHAR  dmFormName[CCHFORMNAME];

i couldnt find what CCHFORMNAME is so i just used the MarshalAs Attribute like this

[MarshalAs(UnmanagedType.ByValTStr, SizeConst=128)]  
public string  dmDeviceName;

for both, could that be the problem?

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

Re: Display Mode

leppie2-Sep-02 3:00

2-Sep-02 3:00

I think the exception lies with string lpszDeviceName being null.

You mite want to redefine:

[DllImport("User32.dll")]
public static extern bool EnumDisplaySettings(StringBuidler lpszDeviceName, int iModeNum, DEVMODE lpDevMode);

Then when calling do StringBuilder devname = new StringBuilder( insert const size here).

Also , many times you need to set the size of a struct. In this case, according to MSDN, you will need to.

Nnamdi Onyeyiri wrote:
i couldnt find what CCHFORMNAME is so i just used the MarshalAs Attribute like this

This you will find the value in the header files, so download the Platform SDK if you dont have it already.

Hope this helps

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Re: Display Mode

Nnamdi Onyeyiri2-Sep-02 3:16