How to marshal char** in struct? - C# Discussion Boards

How to marshal char** in struct?

16-Jan-06 4:21

There are several static functions on the Graphics class. Which one to use depends on what you try to achieve.
Example:

Bitmap b = new Bitmap(100, 100);
using (Graphics g = Graphics.FromImage(b)){
   g.FillRectangle(Brushes.Red, 10, 10, 20, 20);
}

jurot16-Jan-06 3:49

jurot

16-Jan-06 3:49

Hi.

I have struct in C++:

struct MY_STRUCT
{
int x;
int y;
char** arrNames; //array of strings

}

I have function GetMyStruct, which gives me pointer to this struct, but
I can't get the array of strings (MY_STRUCT.arrNames).

MY_STRUCT* GetMyStruct();

In C# :

public struct MY_STRUCT
{
public int x;
public int y;
public string[] arrNames; //array of strings

}

public class MyWrapper
{
[DllImport("MyDll.dll")]
private static extern IntPtr GetMyStruct();
public static MY_STRUCT GetMyStructW()
{
IntPtr p = GetMyStruct();

return (MY_STRUCT) Marshal.PtrToStructure(p, typeof(MY_STRUCT));
}

}

BUT MyWrapper.GetMyStructW() doesn't work. Plllease help.

jurot

Andy Moore16-Jan-06 4:57

Andy Moore

16-Jan-06 4:57

Try changing your c# struct to the following:

public struct MY_STRUCT<br />
{<br />
   public int x;<br />
   public int y;<br />
   public System.IntPtr arrNames;<br />
}<br />
<br />
Your calling code looks like this:<br />
<br />
public class MyWrapper<br />
{<br />
    [DllImport("MyDll.dll")]<br />
    private static extern IntPtr GetMyStruct();<br />
<br />
    public static MY_STRUCT GetMyStructW()<br />
    {<br />
        IntPtr p = GetMyStruct();<br />
        IntPtr pArray;<br />
        IntPtr pString;<br />
        string[] strings;<br />
        MY_STRUCT s;<br />
<br />
        s = (MY_STRUCT)Marshal.PtrToStructure(p, typeof(MY_STRUCT));<br />
<br />
        pArray = s.arrayNames;<br />
<br />
        /*Now you can extract each string one by one as follows*/<br />
        pString = Marshal.ReadIntPtr(pArray);<br />
<br />
        while( pString != null )<br />
        {<br />
              strings[i] = Marshal.PtrToStringUni(pString);<br />
              i++;<br />
              pString = Marshal.ReadIntPtr(pArray);<br />
        }<br />
<br />
        return ( s );<br />
        <br />
        <br />
    }<br />
}

I hope this helps.

Human beings were not meant to sit in little cubicles staring at computer screens all day, filling out useless forms and listening to eight different bosses drone on about about mission statements. -- Peter Gibbons

jurot16-Jan-06 23:15

jurot

16-Jan-06 23:15

Thanks. Finally it works Big Grin | :-D

jurot

jurot17-Jan-06 1:06

jurot

17-Jan-06 1:06

Hi once more,

I found out, that it works fine only if I have MY_STRUCT.arrNames 1 string!

When I have more than one, all strings in the result array are the same.

I guess the cycle

while( pString != null )
{
strings[i] = Marshal.PtrToStringUni(pString);
i++;
pString = Marshal.ReadIntPtr(pArray);
}

in Marshal.PtrToStringUni(pString) is reading still the same value MY_STRUCT.arrNames[0].

jurot

Andy Moore17-Jan-06 11:25

Andy Moore

17-Jan-06 11:25

Try this:

while( pString != null )
{
int byteCount;
strings[i] = Marshal.PtrToStringUni( pString );
i++;
byteCount = System.Text.Encoding.UnicodeEncoding.GetByteCount(strings[i]));
pString = Marshal.ReadIntPtr( pArray, byteCount );
}

I hope this helps.

Andy

Human beings were not meant to sit in little cubicles staring at computer screens all day, filling out useless forms and listening to eight different bosses drone on about about mission statements. -- Peter Gibbons

DataGrid formatting

jeanchalumeau16-Jan-06 3:21

jeanchalumeau

16-Jan-06 3:21

How do I format a string so that it is displayed in a grid with mixed fonts.,just like that!
Thanx.

-- modified at 9:21 Monday 16th January, 2006

Re: DataGrid formatting

Robert Rohde16-Jan-06 4:18

16-Jan-06 4:18

There is no built-in way for this. You will have to create your own custom DataGridColumnStyle and implement it yourself Cry | :((

Re: DataGrid formatting

jeanchalumeau17-Jan-06 3:37

jeanchalumeau

17-Jan-06 3:37

At least I know where to go next! Thanx.

Change file extensions

GermanDM16-Jan-06 3:05

GermanDM

16-Jan-06 3:05

Hi there,
I need some help of changing extensions of files..
My code so far is:

<br />
string filename = Path.Combine(@"C:\Test.txt", @"C:\Test.txt");<br />
filename = Path.ChangeExtension(filename, "old");<br />

the filename variable does equal C:\Test.old but it never actual changes the extension in windows "explorer"...
i tried so many different ways but always get stuck with this problem..
Please help thanks

Best regards

Robert Rohde16-Jan-06 4:17

16-Jan-06 4:17

The functions you are using are just helper functions for correct string manipulation.
You should use either
File.Move(filename, Path.ChangeExtension(filename, "old"));
or
new FileInfo(filename).MoveTo(Path.ChangeExtension(filename, "old"));

GermanDM16-Jan-06 19:36

GermanDM

16-Jan-06 19:36

Thanks Robert,
this is the code i used and it works perfectly

<br />
string filename = lboxFiles.Items[x].ToString();<br />
new FileInfo(filename).MoveTo(Path.ChangeExtension(filename,cmbxRenExt.SelectedItem.ToString()));<br />

One question though,if i use the MoveTo isnt it bit slower than actually just renaming the extension because now it moves over replacing every file?
the reason im asking is because i have to scan and change over 500000 file extensions lol...
Thanks for ur help i really appreciate it... Smile | :)

Regards

GermanD

Robert Rohde16-Jan-06 19:49

16-Jan-06 19:49

Move is intelligent. As long as you remain on the same drive Move is not really moving all bits of a file but is just changing an entry somewhere in the file system. It's like in Explorer. There you can also 'move' files between directories with nearly no time loss.
But 500000 will nevertheless take some time probably.