Transfer string data to unmanaged buffer

[Guest]

I declared a struct with fixed size buffers to send it to an unmanaged function

[StructLayout (LayoutKind.Sequential)]
unsafe struct RCSTKAS
{
public fixed Byte xValue1 [12];
public fixed Byte xValue2 [30];
...
}

Before calling the external function that takes the struct as one of its
parameters I have to load some of the members. How can I copy for instance
the data of a String or a Byte[] to xValue1? I found no other solution than
writing an unsafe routine that defines 2 pointers and does the copying. Is
there a more elegant way to do this?

BTW: The other direction, copying data from the buffer to a String is no
problem thow as string offers a constructor taking a SByte*.

 

[Mattias Sjögren]

How can I copy for instance
the data of a String or a Byte[] to xValue1?

How about one element at a time in a simple loop?

for (int i = 0; i < source.Length; i++)
dest.xValue1 = source;


Mattias

 

[Greg Young [MVP]]

Try using Buffer.BlockCopy() for the byte arrays, it is also faster than the
unmanaged code.

For strings the various Encoding objects return a byte array for you.
System.Text.ASCIIEncoding
http://msdn2.microsoft.com/en-US/library/system.text.asciiencoding.aspx as
an example. You can get a byte array using the GetBytes method

Cheers,

Greg

 

[Greg Young [MVP]]

Also for performance questions on various ways of dealing with byte data ..

http://www.eggheadcafe.com/articles/20050325.asp
and follow up ..
http://geekswithblogs.net/gyoung/archive/2006/04/23/76161.aspx

Cheers,

Greg

 

[Mattias Sjögren]

Try using Buffer.BlockCopy() for the byte arrays, it is also faster than the

unmanaged code.

It wont work for fixed size buffers since they aren't proper arrays.


Mattias

 

[Greg Young]

Correct missed the fixed, the fastest code then is the last example on my
blog.

Cheers,

Greg

 

[Guest]

Yes, I thought of that. As I have to fill the receiving buffer with trailing
spaces, the complete loop would be

Byte[] abBytes = Encoding.Default.GetBytes (strValue1);
for (Int32 i = 0; i < 12; i++)
{
if (i < abBytes.Length)
rcstkas.xValue1 = abBytes;
else
rcstkas.xValue1 = 0x20;
}

Instead of writing that 50 times for 50 differnt strings I decided the code
would be more readable by writing 50 times

ByteArrayToBuffer (rcstkas.xValue1, Encoding.Default.GetBytes
(strValue1), 12);

Another question arising : Is there any language construct to avoid
repeating the length of the unmanaged buffer as a literal, 12 in this example?
--
Regards
Burkhard

How can I copy for instance
the data of a String or a Byte[] to xValue1?

How about one element at a time in a simple loop?

for (int i = 0; i < source.Length; i++)
dest.xValue1 = source;


Mattias

 

[Guest]

fixed(byte *a = destination) {
fixed(byte *b = buffer) {
while(j < TimesToRun) {
byte *current = (byte *) b;
byte *dest = a;
byte *end = current + buffer.Length;
while(current < end) {
*dest = *current;
current ++;
dest++;
}
j++;
}
End = DateTime.Now;
}
}

being the fastest example.

Cheers,

Greg

Correct missed the fixed, the fastest code then is the last example on my
blog.

Cheers,

Greg

 

[_DD]

It wont work for fixed size buffers since they aren't proper arrays.


Mattias

Mattias,

Nice reference to books on interop on your site. Just wanted to let
you know about a new book from Apress by Bruce Bukovics called
..NET 2.0 Interop Recipes. ISBN 1590596692.

Links (best prices):
http://www.bookpool.com/sm/1590596692
http://www.nerdbooks.com/item.php?id=1590596692

I'm not affiliated in any way. In fact, I'm only about 60 pages into
it, but so far it's great. Very pracical, very clear, with real-world
examples.

 

[Mattias Sjögren]

Nice reference to books on interop on your site. Just wanted to let

you know about a new book from Apress by Bruce Bukovics called
.NET 2.0 Interop Recipes. ISBN 1590596692.

Thanks, I appreciate the tip. Hadn't seen that book before. Now I just
have to find time to update the site, it's way outdated.


Mattias