Re: Calling a C function from C# and getting values from it. - C# Discussion Boards

Calling a C function from C# and getting values from it.

1-Jul-09 1:18

Sorry, can't really offer a good answer.

To me it looks like you can't really do anything to help it yourself. I'm thinking maybe the comboBox and listBox handle DataSources differently and that is causing the delay - but I don't know that for sure.

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shivapriyak30-Jun-09 2:42

shivapriyak

30-Jun-09 2:42

I have a C function of format:
func1(double param[], int size);

This function is called from C# code the following syntax:
[DllImport("first.dll", EntryPoint = "func1", CallingConvention = CallingConvention.StdCall)]
public static extern int func1(ref double param[], int size);

The function 'func1' takes two parameters: the array in which values should be filled up from C dll and 'size' which tells the number of values to fill in the array.
Now if the param[] array is declared as param[] = new double[5]; and the 'size' parameter is given as 10, still the function passes.
Wherase the same scenario in direct C application, gives error saying "Array size(i.e. 5) is lesser than the number of values to fill(i.e. 10)".

I am not able to reproduce the same behavior in .Net. Can anybody help me with it?

Re: Calling a C function from C# and getting values from it. [modified]

DaveyM6930-Jun-09 3:26

DaveyM69

30-Jun-09 3:26

~~My guess (I haven't checked) is that the number of bits used in C for the double may be 32, but in C# it's 64.~~

Hmmm, it appears that they are both 8 bytes (64 bit) Confused | :confused:

Dave
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modified on Tuesday, June 30, 2009 9:36 AM

Re: Calling a C function from C# and getting values from it.

shivapriyak30-Jun-09 3:34

shivapriyak

30-Jun-09 3:34

ok..how to ensure that both the sizes are the same..i mean if i declare array of size 5 (5 x 8 = 40bytes) should be the same in C# also.

Re: Calling a C function from C# and getting values from it.

DaveyM6930-Jun-09 3:39

DaveyM69

30-Jun-09 3:39

I've just edited my previous reply as it appears that double is 8bytes (64 bits) in managed and unmanaged environments Confused | :confused:

Re: Calling a C function from C# and getting values from it.

Luc Pattyn30-Jun-09 4:03

Luc Pattyn

30-Jun-09 4:03

Hi Dave,

native float typically uses 4 bytes, and double doubles that, hence the name.
managed float always uses 4 bytes, and double 8 bytes.

Smile | :)

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Re: Calling a C function from C# and getting values from it.

Luc Pattyn30-Jun-09 4:09

Luc Pattyn

30-Jun-09 4:09

Hi,

three remarks:

1.

shivapriyak wrote:
public static extern int func1(ref double param[], int size);

I doubt you need the ref there. Objects (array is object) get passed by reference, so what you get is a pointer to the data anyway. With "ref" you get a pointer to a pointer, which you would then have to accept as a double**param.

2.

I typically don't rely on automatics marshaling, instead I use GCHandle class to pin the object and get its pointer into an IntPtr, then pass that to the native world. However, I am not saying your way could not work (without ref!).

3.

shivapriyak wrote:
in direct C application, gives error saying "Array size(i.e. 5) is lesser than the number of values to fill(i.e. 10)".

How the heck can the function now that???

Smile | :)

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Re: Calling a C function from C# and getting values from it.

shivapriyak30-Jun-09 20:03

shivapriyak

30-Jun-09 20:03

1. I have tried removing 'ref' and giving just double param[] in PInvoke...it didn't work Frown | :(

2. Tried using GCHandle class as below:

int func1(double param[],int size)
{
GCHandle handle = GCHandle.Alloc(param, GCHandleType.Pinned);
Pinvoke.func1(handle.AddrOfPinnedObject(),size);
}
The Pinvoke class is as:
[DllImport("myFile.dll",EntryPoint="func1",CallingConvention = CallingConvention.StdCall)]
public static extern int func1(IntPtr handle, int size);

But it didn't work...is this correct way? or do i need to tweak at some place.

Thanks,
Priya.

Re: Calling a C function from C# and getting values from it.

Luc Pattyn30-Jun-09 22:57

Luc Pattyn

30-Jun-09 22:57

Hi,

shivapriyak wrote:
it didn't work

that does not tell me much

shivapriyak wrote:
int func1(double param[],int size)
{
GCHandle handle = GCHandle.Alloc(param, GCHandleType.Pinned);
Pinvoke.func1(handle.AddrOfPinnedObject(),size);
}

looks good, except when done you need to free the GCHandle.

Smile | :)

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SQLite in C#

stancrm30-Jun-09 2:35

stancrm

30-Jun-09 2:35

Hello. I'm using SQLite and System.Data.SQLite.
If I create a new table, the file size is 2KB.
After insert 1000 records, the file size will be 34KB.
If I delete all record, the file size remain 34KB.
If I send SELECT command, the table is empty.

Why ?

Thanks.

Re: SQLite in C#

Pete O'Hanlon30-Jun-09 2:39

Pete O'Hanlon

30-Jun-09 2:39

stancrm wrote:
Hello. I'm using SQLite and System.Data.SQLite.
If I create a new table, the file size is 2KB.
After insert 1000 records, the file size will be 34KB.
If I delete all record, the file size remain 34KB.
If I send SELECT command, the table is empty.

Why ?

Because a delete does not reclaim disk space (that would be a very wasteful use of system resources). Databases don't tend to allocate space as records are added, they allocate space in blocks and then insert records to the allocated space (it's much more efficient for them to do this as it results in less I/O activity on the disk).

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Re: SQLite in C#

SeMartens30-Jun-09 2:41

SeMartens

30-Jun-09 2:41

Hi,

you are getting an empty table because you deleted all records before. The file size of the database will not shrink if you delete rows because that would mean a reordering of the internal structure (db-records are stored in pages etc.). Some databases (especially for mobile applications) offer a shrink-command. This will result in the reordering and a smaller file.

At least: Please choose the correct forum for your question, I think "General Database" would be a better place.

Regards
Sebastian

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How to Upload large size file to server

wasimsharp30-Jun-09 2:21

wasimsharp

30-Jun-09 2:21

Hi friend i am creating WindowDesktop application that will upload a large size of file to the server.
now when i upload file of small size its uploaded with no problem but when i upload large size of 62Mb or so it throw exception. can any body tell me that how can i upload large file and can i also pause uploading and resume Uploading feature
<pre

filestream="" stream="new" filestream("c:\\xyz.zip",="" filemode.open);

="" byte[]="" buffer="new" byte[stream.length];
="" int="" i="0;
" while="" ((i="stream.Read(buffer,0," buffer.length))>0)
="" {

="" ftpwebrequest="" request="(FtpWebRequest)FtpWebRequest.Create("ftp://ftp.abc.com/"" +="" path.getfilename("c:\\xyz.zip"));
="" try
="" {
="" request.method="WebRequestMethods.Ftp.UploadFile;
" request.credentials="new" networkcredential("demo123",="" "demo123");
="" request.usepassive="true;
" request.usebinary="true;
" request.keepalive="false;
"
="" request.timeout="int.MaxValue;

" reqstream="request.GetRequestStream();
" reqstream.write(buffer,="" 0,="" buffer.length);
="" reqstream.beginwrite(buffer,="" buffer.length,="" callback,="" "aa");
="" reqstream.close();
="" }
="" catch="" (exception="" ex)
="" stream.close();="">

i use both Write and BeginWrite method

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Vimalsoft(Pty) Ltd30-Jun-09 2:28

30-Jun-09 2:28

We cannot know unless you tell us what Expetion you are getting

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wasimsharp30-Jun-09 2:33

wasimsharp

30-Jun-09 2:33

Hi Vuyiswa Maseko

Error is "Unable to write data to the transport connection: An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full."

WANTED wasim khan(Killed 50 Innocent Buggs, Distroyed 200 Exception, make 5 Project Hostage) any Compnay Hire him will pay 30,000. Best place where u can get him is Sorcim Technologies Murre Road RWP

Vimalsoft(Pty) Ltd30-Jun-09 2:37

30-Jun-09 2:37

musefan is Right increase the Buffer and see what happends

musefan30-Jun-09 2:40

30-Jun-09 2:40

I'm actually suggesting to reduce the buffer size.. but I assume that is what you meant anyway Wink | ;)

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Vimalsoft(Pty) Ltd30-Jun-09 2:42

30-Jun-09 2:42

Its one of those Days Smile | :)

today its the Final day of my Project Smile | :)

Am tired

musefan30-Jun-09 2:43

30-Jun-09 2:43

I see

Just out of interested what is your project? is it a course project?

Life goes very fast. Tomorrow, today is already yesterday.

Vimalsoft(Pty) Ltd30-Jun-09 2:47

30-Jun-09 2:47

My Company is in Education Industry

My Department Smile | :)

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===============

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musefan30-Jun-09 2:58

30-Jun-09 2:58

Interesting Wink | ;)

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musefan30-Jun-09 2:33

30-Jun-09 2:33

I have not really read your code but my first guess would be your buffer array size is causing the issue. The buffer should not contain all the data else you may as well use the stream itself.

Try a buffer size of 1024 - that's a common size that is used.

Life goes very fast. Tomorrow, today is already yesterday.

wasimsharp30-Jun-09 2:42

wasimsharp

30-Jun-09 2:42

yes i set the buffer size to 1024
it working but in process it threw exception couple of time "The underlying connection was closed: An unexpected error occurred on a receive."

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musefan30-Jun-09 3:01