C# Discussion Boards - CodeProject

PIEBALDconsult13-Jul-09 8:18

PIEBALDconsult

13-Jul-09 8:18

XML is case-sensitive.

Not Active13-Jul-09 8:19

Not Active

13-Jul-09 8:19

What do you mean "it is case sensitive"? The element names? Thats because XML is case sensitive.

only two letters away from being an asset

0x3c013-Jul-09 8:43

0x3c0

13-Jul-09 8:43

As has been said before, XML is case-sensitive. An icky solution would be to pass it the lower-case string representation of your XML document. You could also iterate through the descendants in xmlDoc, create a new XNode based on each descendant (except with the lower-case name) add them to a new XDocument and work with that for your query.

A side note: look at what you do with your query, particularly the Where() method. You could actually merge that into the query itself, making the code look more aesthetically pleasing. AFAIK, you can do most of what you would normally do with a List, with an IEnumerable

Between the idea
And the reality
Between the motion
And the act
Falls the Shadow

Not Active13-Jul-09 10:19

Not Active

13-Jul-09 10:19

Computafreak wrote:
As has been said before...

Then why say it?

Custom XPath Functions - performing case-insensitive searches in XPath expressions[^]

only two letters away from being an asset

Unmanaged DLL: C# variable for C++ char**

0x3c013-Jul-09 19:54

0x3c0

13-Jul-09 19:54

Wow, I didn't know about that. I've never really looked into XPath queries and functions, I'll have to do that now. Thanks for the tip

Between the idea
And the reality
Between the motion
And the act
Falls the Shadow

belier113-Jul-09 7:06

13-Jul-09 7:06

Hello to all. My first thread on this forum. I'm really new with C# and I got stuck with a pointer. I've done some research with no success.

I'm making an application that works with buffers. I have to call some C++ functions with data pointers as arguments. I'm trying to not use unsafe code.
One of the functions have two parameters of type char*. I've defined on C# two buffers:

byte[] Buffer1 = new byte[SIZE];
byte[] Buffer1 = new byte[SIZE];

On the dllimport I use marshaling:
....
[MarshalAs(UnmanagedType.LPArray)] byte[] buffer1,
[MarshalAs(UnmanagedType.LPArray)] byte[] buffer2,
....

These two buffers are filled by the C++ function.
In order to retrieve the data of the buffers, I use another C++ function. This function returns in a parameter the last buffer filled:

void FillBuff(char **Pbuff);

Pbuff is a pointer to one of the byte[] buffers defined above.
The problem is that I don't know how to define a C# to assign the pointer returned by the C++ function and accessing to the buffer's content.

Any suggestion?

Thanks in advance

Luc Pattyn13-Jul-09 7:28

Luc Pattyn

13-Jul-09 7:28

Hi,

when mixing managed code and unmanaged/native code, I recommend you let the managed side do the array allocations (so they are real objects); doing so, all you need is one of two things:

1. the fixed keyword, which is OK if the array is used natively only while the native function executes; here the P/Invoke prototype takes a pointer where the native code expects a pointer.

2. the GCHandle class, which allows you to:
- pin the object, so the GC can no longer move it around
- get a pointer to it
- pass that pointer to the native function
- when done, free the GCHandle object.
Here the P/Invoke prototype takes an IntPtr where the native code expects a pointer.

BTW: for strings, there are easy shortcuts:
- read-only strings can be passed as string and accepted as char*
- read/write strings can be passed as StringBuilder (call ToString when done)

Smile | :)

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belier113-Jul-09 9:47

13-Jul-09 9:47

Thanks for answering.

They are not strings, are image buffers. I use a ping-pong strategy: One buffer for grabing image, the other for processing it, both alternating. I declare both buffers at the C# application and pass them to the C++ DLL. The image grabbing routine passes back the pointer to the buffer holding the last image grabbed. Is this parameter which I don't know how to declare and manage at the C# level. I'll like to have the pointer accessible everywhere, as I have to draw the image and process it.

C#: Buffer1 and Buffer2 and Pointer to active buffer
C++: Fills Buffer1 and Buffer2 and passes back pointer to last grabbed buffer

Using fixed keyword doesn't wrok for me, as I want to have a "global" variable. About GCHandle, I'm not sure if I'll be able to use it for using the Marshal.Copy:

System.Drawing.Imaging.BitmapData bmpData =
bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite,
bmp.PixelFormat);

// Get the address of the first line.
IntPtr ptr = bmpData.Scan0;

int bytes = bmp.Width * bmp.Height;

// Copy the RGB values back to the bitmap
System.Runtime.InteropServices.Marshal.Copy(PBuffer, 0, ptr, bytes); // TRANSFERING HERE THE CONTENT OF THE GRABBED BUFFER TO THE BITMAP IN ORDER TO PAINT IT

// Unlock the bits.
bmp.UnlockBits(bmpData);

Thanks in advance for helping

Luc Pattyn13-Jul-09 10:04

Luc Pattyn

13-Jul-09 10:04

Hi,

when fixed doesn't fit the requirements, GCHandle will. I tend to almost always use GCHandle, even when fixed would suffice. One of the advantages is you typically don't need to copy the data AT ALL, since the scenario is:
1. managed world creates an array
2. uses GCHandle to pin and get the pointer
3. passes it to native world, which fills the buffer, then returns
4. managed world frees GCHandle and uses the array.
See, no copy involved, hence also no performance hit.

If the buffer is really the entire pixel data of a Bitmap, I would try and use Bitmap.Lockbits to pin and get the pointer (it does what GCHandle does for a general object), pass that pointer to the native world, and all would be OK again without a copy operation, provided your native code:
1. applies the right byte ordering within a pixel
2. applies the right pixel ordering
3. applies the right bitmap stride (normally no problem if scanlines are a multiple of 4 bytes, which is true for 32-bit pixels, or image widths that are multiples of 4).

My number 1 rule in image processing is: avoid copy operations.

Smile | :)

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belier113-Jul-09 11:07

13-Jul-09 11:07

Hi Luc.

The problem here is that is the C++ DLL who fills the buffer. The C# application doesn't know which buffer has been filled. Is for this reason that I need to call a function to get the pointer to the buffer. It's important for me to let the native world (C++) control the flow of grabbing images on alternate buffers in order to improve the processing speed of the system (real time image processing). If I don't succeed on getting the buffer pointer I'll try another thing.

I'll keep you informed.
Thanks for your time. Big Grin | :-D

Luc Pattyn13-Jul-09 11:12

Luc Pattyn

13-Jul-09 11:12

Hi,

that is a secondary issue. Let the managed side provide one or more buffers to the native world, which fills one and tells which one. You don't need to return a pointer for that, a simple ID could do; but if you do return a pointer, keep a Dictionary that maps pointers to Bitmaps, and perform a pointer look-up.

However, if there are only two bitmaps, and you alternate them, there is no need to return anything, alternation is quite predictable!

Smile | :)

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belier114-Jul-09 1:10