Re: Display Mode - SOLUTION :) - C# Discussion Boards

2-Sep-02 3:31

Nnamdi Onyeyiri wrote:
dont think so, i tried entering a value for that, and it did not work, it gavethe same exception. i used null, because that is what was used in the article i gave the link for.

Still try using StringBuilder as u CAN pass null as a value.

Nnamdi Onyeyiri wrote:
is that installed with the default settings for vs.net install?

If u install VC++ , else just look for a dir in program files with many *.h files Smile | :)

I had a look and that is a pretty viscious struct Smile | :)

. Im not sure what a BCHAR is though. Im gonna try do something in C# and see what i come up with. Can you perhaps mail me what u have done so far?

Cheers Smile | :)

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Re: Display Mode

Nnamdi Onyeyiri2-Sep-02 3:39

Nnamdi Onyeyiri

2-Sep-02 3:39

leppie wrote:
I had a look and that is a pretty viscious struct . Im not sure what a BCHAR is though. Im gonna try do something in C# and see what i come up with. Can you perhaps mail me what u have done so far?

sure, but ill need your email address Smile | :)

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

leppie2-Sep-02 4:02

2-Sep-02 4:02

DEVMODE dm = new DEVMODE();
dm.dmSize = (short)Marshal.SizeOf(typeof(DEVMODE));
int mode = 0;
while (EnumDisplaySettings(null, mode++, ref dm) != 0)
{
	Console.WriteLine("{0}x{1}, {2}bits {3}hz",
		dm.dmPelsWidth, dm.dmPelsHeight, dm.dmBitsPerPel, dm.dmDisplayFrequency);
}

[DllImport("user32.dll", CharSet=CharSet.Ansi)]
static extern int EnumDisplaySettings(StringBuilder devname, int mode, ref DEVMODE devmode);

public struct DEVMODE 
{
	[MarshalAs(UnmanagedType.ByValTStr, SizeConst=32)]
	public string dmDeviceName; 
	public short dmSpecVersion; 
	public short dmDriverVersion; 
	public short dmSize; 
	public short dmDriverExtra; 
	public int  dmFields; 
	public short dmOrientation;
	public short dmPaperSize;
	public short dmPaperLength;
	public short dmPaperWidth;
	public short  dmScale; 
	public short  dmCopies; 
	public short  dmDefaultSource; 
	public short  dmPrintQuality; 
	public short  dmColor; 
	public short  dmDuplex; 
	public short  dmYResolution; 
	public short  dmTTOption; 
	public short  dmCollate; 
	[MarshalAs(UnmanagedType.ByValTStr, SizeConst=32)]
	public string  dmFormName; 
	public short  dmLogPixels; 
	public int  dmBitsPerPel; 
	public int  dmPelsWidth; 
	public int  dmPelsHeight; 
	public int  dmDisplayFlags; //funny union??
	//public int  dmNup;
	public int  dmDisplayFrequency; 
	public int  dmICMMethod;
	public int  dmICMIntent;
	public int  dmMediaType;
	public int  dmDitherType;
	public int  dmReserved1;
	public int  dmReserved2;
	public int  dmPanningWidth;
	public int  dmPanningHeight;
}

This works Smile | :)

Note the union ???? looks like it combines 2 int 's ???

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Nnamdi Onyeyiri2-Sep-02 4:51

Nnamdi Onyeyiri

2-Sep-02 4:51

thanks a lot! ive been puzzled over this for the last few hours. Big Grin | :-D

leppie wrote:
This works Note the union ???? looks like it combines 2 int 's ???

im not sure what you mean.

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leppie2-Sep-02 5:02

2-Sep-02 5:02

Im not really sure what a union in C++ does, it appears to join 2 variables into one, hence the commented dmNup. Can anyone C++ person please explain this in C# terms?

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Paul Riley2-Sep-02 5:57

Paul Riley

2-Sep-02 5:57

A union uses the same piece of memory for two different variables.

For example

struct INTCHARS
{
    char hi;
    char midhi;
    char midlo;
    char lo;
};


union FOURBYTES
{
    INTCHARS ch;
    int i;
};


FOURBYTES four;
four.ch.hi = 1;
four.ch.midhi = 1;
four.ch.midlo = 1;
four.ch.lo = 1;
four.i = 0;

Now each part of four.ch is 0.

Going back a while since I used one of these. Smile | :)

Paul

leppie2-Sep-02 6:12

2-Sep-02 6:12

Thx,

From what i can see is that unions are class like structures in a struct or class allowing easy retriaval/setting of inner variables. I have been using SequintialLayout classes todo this. Im not sure if we are talking the same thing, but I guess thats why the are not included in C#.

Cheers Smile | :)

MYrc : A .NET IRC client with C# Plugin Capabilities. See
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Paul Riley2-Sep-02 8:00

Paul Riley

2-Sep-02 8:00

The big difference between a union and a struct is that changing one inner variable in a union will change all of them because they share the same space in memory.

As C++ came into play, unions became less useful, classes and pointers could be used to the same effect.

When PCs with more than 50 bytes of spare memory came out, unions again lost some usefulness. Wink | ;)

Likewise properties haven't done unions any favours, you can now reference the same variable in different ways through get/set properties.

So I wouldn't be surprised if C# didn't have an equivalent, though there are times when it wouldn't go amiss.

Paul

Paul Ingles2-Sep-02 7:52

Paul Ingles

2-Sep-02 7:52

From what I understand (I also was looking into unions recently -- trying to DllImport DnsQuery_A) a union is a UDT which allows for one datatype or another, so if you specify it with a String or Int32 it would let the value be one of the two. At least that was what I took it to mean Smile | :)

I'm not aware of a native C# equivalent but would be glad to know of one!

--
Paul
"I need the secure packaging of Jockeys. My boys need a house!"
- Kramer, in "The Chinese Woman" episode of Seinfeld

MS Messenger: paul@oobaloo.co.uk
Sonork: 100.22446

James T. Johnson2-Sep-02 9:38

James T. Johnson

2-Sep-02 9:38

As others have said a union just uses the same memory space to hold each of the types (thus only allowing one of them to be used at a time).

Typically when you are dealing with a union you have to break it out into its own datatype so that you can properly use it in code. Otherwise you could be having to use the same variable for two vastly different things such as a pointer to a string and a byte which will be hard to do when dealing with a single member.

To create a union in C#:

[StructLayout(LayoutKind.Explicit)]
public struct myUnion
{
  [FieldOffset(0)] string FieldA;
  [FieldOffset(0)] bool FieldB;
  [FieldOffset(4)] int FieldC;
  [FieldOffset(4)] long FieldD;
  [FieldOffset(12)] int Foo;
  [FieldOffset(12)] char Bar;
  [FieldOffset(12)] float Baz;
}

The numbers used will position where in memory each field will be placed, using the technique you can also create multiple unions as I did above (FieldA and FieldB; FieldC and FieldD; and Foo, Bar, and Baz; are all unions, where only one of the members can be used).

Hope that makes sense.

James
"And we are all men; apart from the females." - Colin Davies

Array of strings to old DLL?

Paul Riley2-Sep-02 9:52

Paul Riley

2-Sep-02 9:52

That is very cool, James, nice one! Cool | :cool:

Paul

EdgarBM1-Sep-02 23:25

1-Sep-02 23:25

Hi,
I have an old DLL developped on VC++ 6.0. It was designed to work with VB and VC code. The problem always has been two special parameters which where an array of vaules. One was an array of doubles and the other an array of strings.
It was hard, but I solved it using the SAFEARRAY structure, this way:
Method (..., SAFEARRAY FAR *doubleArray, SAFEARRAY FAR *stringArray, ...)

-> To call the library from VB code I only should do:

Dim dbArray() as double<br />
Dim stArray() as string<br />
Redim dbArray(5)<br />
dbArray(0) = 3.4<br />
...<br />
'and so to strings

->To call it from VC it was more difficult:

char sMatriz[1][256/*128x2, chars doubled!*/];<br />
strcpy (sMatriz[0], "H E L L O "); //the space represents the NULL between the string characters due to compatibility with COM ; not for doubles array<br />
LPSAFEARRAY sS = new struct tagSAFEARRAY;<br />
sS->pvData=sMatriz;<br />
sS->rgsabound->cElements = 1;<br />
//...and I passed the reference of the LPSAFEARRAY: <br />
Method (..., &sD, &sS, ...)

THE PROBLEM:
---------------------
Now I want this library to be used on C# or VB.NET, but I don't know the way to instantiate and pass those parameters. Any chance I get an exception like this:

System.NullReferenceException<br />
Exception Details: Object reference not set to an instance of an object.

I pass those parameters like:

string[] sA = new string[5]; double[] dA = new double[5];<br />
Method (..., dA, sA,...)

...and if I modify the library taking out those params (ignoring them), everything works fine.

Does anyone knew how can I solve this problem? Is there any special way to pass those parameters?, anything before changing the library? I really need those params in the library!

Thank you in advance, (thanks if you read all the text!)
Edgar

Edgar Berengena Moreno
Software Engineer
Appeyron Research

Stephane Rodriguez.1-Sep-02 23:38

Stephane Rodriguez.

1-Sep-02 23:38

A SAFEARRAY in C++ like this :

HRESULT GetItems([in] BSTR bstrLocation, [out] SAFEARRAY(VARIANT)* pItems);

is marshalled back and forth with C# declaration like this in your interface :

[ComImport]
[Guid("73EB4AF8-BE9C-4b49-B3A4-24F4FF657B26")]
public interface IMyStorage  
{
  [DispId(2)]
  void GetItems( [In, MarshalAs( UnmanagedType.BStr )] String bstrLocation, 
         [Out, MarshalAs( UnmanagedType.SafeArray, SafeArraySubType = VarEnum.VT_VARIANT )] out Object[] Items );

...
}

Further details.

And I swallow a small raisin.

EdgarBM2-Sep-02 1:14

2-Sep-02 1:14

Thanks,

...but I can't improve anything with this! I'm trying to pass an Object[] to the library but I'm still getting the same exception.

Is there anymore information or runnig sample which solves this problem?, does anyone know it??

Thank you again,
Edgar

Edgar Berengena Moreno
Software Engineer
Appeyron Research

Stephane Rodriguez.2-Sep-02 1:33

Stephane Rodriguez.

2-Sep-02 1:33

Can you try the following code :

string[] MyString = {"Hello", "and", "welcome", "to", "my" , "world!"};

I am not sure the exception you have is a marshalling issue.

And I swallow a small raisin.

EdgarBM2-Sep-02 1:52

2-Sep-02 1:52

Thank you, Stephane, but It doesn't work. I always thought this was the correct solution, but it gaves me the System.NullReferenceException exception.

If you have any other idea, please let me know.
Thank you,
Edgar

Edgar Berengena Moreno
Software Engineer
Appeyron Research

leppie2-Sep-02 1:50

2-Sep-02 1:50

Hi maybe I can help.

1. Create arrays, like normal
2. Before calling function, foreach array, allocate mem, copy array to pointer and pass the pointer.
3. when the array returns copy the pointer back to the array.

For example: From MDSN

// array ByRef
int[] array2 = new int[ 10 ];
int size = array2.Length;

IntPtr buffer = Marshal.AllocCoTaskMem( Marshal.SizeOf( size )
   * array2.Length ); // or Marshal.AllocHGlobal (COM or not)
Marshal.Copy( array2, 0, buffer, array2.Length );

int sum2 = LibWrap.TestRefArrayOfInts( ref buffer, ref size ); // replace this with your function replaceing arrays with IntPtr

if( size > 0 )
{
   int[] arrayRes = new int[ size ];
   Marshal.Copy( buffer, arrayRes, 0, size );
   Marshal.FreeCoTaskMem( buffer ); //or Marshal.FreeHGlobal
}

Now just do this to each array. Unfortunately u dont give the whole function as defined in a header file, so I cant gaurentee this will work, but it works in my case when normal marshalling wouldnt work Smile | :)

Hope this helps

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

EdgarBM2-Sep-02 2:10

2-Sep-02 2:10

Thanks for your reply, Leppie.

The only problem is that I'm working with string arrays too, so the Copy method of Marshall can't be applied.
I can't say if it works or doesn't work because I need to manage the string array too so keeps receiving the exception...although it seems to work for the double[] (maybe I hope)!!

Any idea for the string array?

PS: the unmanaged DLL parameters (VC++ 6.0 DLL) are defined as
SAFEARRAY FAR *doubleArray, SAFEARRAY FAR *stringArray
...these are the conflicting ones.

Thank you again,
Edgar

Edgar Berengena Moreno
Software Engineer
Appeyron Research

leppie2-Sep-02 2:33

2-Sep-02 2:33

Hi try this, glad to see double[] works Smile | :)

Try this:

ArrayList tags = new ArrayList();
do 
{
  string tag = Marshal.PtrToStringUni(ptag); 
  // ptag is pointer to string[], make sure about unicode/ansi, i assume unicode
  if (tag == "") break;
  else 
  {
    tags.Add(tag);
    ptag = new IntPtr(ptag.ToInt32() + Marshal.SizeOf(tag));
  }
}
while(true);

This reversse can be done if u need to "feed" the function with the string[].

Hope this works

MYrc : A .NET IRC client with C# Plugin Capabilities. See
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EdgarBM2-Sep-02 21:44

2-Sep-02 21:44

Hi,
I'm trying your second code but I'm having problems and I don't know if I'm doing it quite well. That's what I'm trying now:

For the double[]:

<br />
IntPtr buffer = Marshal.AllocCoTaskMem( Marshal.SizeOf( cantidad ) * sVN.Length); // or Marshal.AllocHGlobal (COM or not)      <br />
Marshal.Copy( sVN, 0, buffer, sVN.Length );<br />

...and for the string[]:

<br />
IntPtr ptag = new IntPtr ();<br />
ptag = Marshal.StringToHGlobalAnsi ("maybe...");<br />
ArrayList tags = new ArrayList();<br />
do <br />
{<br />
	string tag = Marshal.PtrToStringAnsi (ptag); //PtrToStringUni (ptag);    // ptag is pointer to string[], make sure about unicode/ansi, i assume unicode  <br />
	if (tag == "") break;  <br />
	else   <br />
	{    <br />
		tags.Add(tag);    <br />
		ptag = new IntPtr(ptag.ToInt32() + <br />
		Marshal.SizeOf(Marshal.StringToHGlobalAnsi (tag)));  <br />
	}<br />
}while(true);

And I define the DLL Function like:
Method (..., ref IntPtr sbufN, ArrayList sbufC, ...);

What am I doing wrong?

Thank you again for your dedication,
Edgar

__________________________________________
Edgar Berengena Moreno
Software Engineer
Appeyron Research

leppie3-Sep-02 2:19