Help With Calling Unmanaged C Code

[jamil]

I have a Windows DLL written in C that I need to call in VB code. The
function has two parameters and must modify the character array for
just one of the parms. A simplified example of C code I wish to call
from test.dll is as follows:

__declspec(dllexport) void CopyString (char *in, char *out)
{
strcpy_s(out, strlen(in), in);
return;
}

My question is how do I call this from VB? Will I have to use an
IntPtr, a Char array, or something else? I know I must allocate memory
for the out parameter, but I would prefer to do this in my managed VB
code.

Will my declaration look like the following or something else?:

<System.Runtime.InteropServices.DllImport("test.dl l")_
Private Shared Sub CopyString(ByVal in As Char(), _
ByVal out As Char())
End Sub

TIA

[Tom Shelton]

On 2008-05-24, ja***@onepost.net <ja***@onepost.netwrote:

I have a Windows DLL written in C that I need to call in VB code. The
function has two parameters and must modify the character array for
just one of the parms. A simplified example of C code I wish to call
from test.dll is as follows:

__declspec(dllexport) void CopyString (char *in, char *out)
{
strcpy_s(out, strlen(in), in);
return;
}

My question is how do I call this from VB? Will I have to use an
IntPtr, a Char array, or something else? I know I must allocate memory
for the out parameter, but I would prefer to do this in my managed VB
code.

Will my declaration look like the following or something else?:

<System.Runtime.InteropServices.DllImport("test.d ll")_
Private Shared Sub CopyString(ByVal in As Char(), _
ByVal out As Char())
End Sub

TIA

Well... Assuming that this is a __stdcall function - then, it would
look something like:

Declare Ansi Sub CopyString Lib "test.dll" (ByVal in As String, ByVal out As System.Text.StringBuilder)

HTH

--
Tom Shelton

[jamil]

On Sat, 24 May 2008 09:33:19 -0700, Tom Shelton
<to*********@YOUKNOWTHEDRILLcomcast.netwrote:

>Well... Assuming that this is a __stdcall function - then, it would
look something like:

Declare Ansi Sub CopyString Lib "test.dll" (ByVal in As String, ByVal out As System.Text.StringBuilder)

HTH

It is doing a bit more than making standard function calls. The intent
behind my example was to show the parms.

I was not setting the character set though, and I modified my
declaration as follows:

<System.Runtime.InteropServices.DllImport("test.dl l",
CharSet:=CharSet.Ansi)_
Private Shared Sub CopyString(ByVal sIn As String, _
ByVal sOut StringBuilder)
End Sub

The issue I run into is that when this function is called, I receive a
generic error as follows:

Test.vshost.exe has encountered a problem and needs to close. We are
sorry for the inconvenience.

I'm not receiving anything useful in indicating what the issue is.

[Tom Shelton]

On May 24, 2:00*pm, [e-mail] wrote:

On Sat, 24 May 2008 09:33:19 -0700, Tom Shelton

<[e-mail]:

Well... *Assuming that this is a __stdcall function - then, it would
look something like:

Declare Ansi Sub CopyString Lib "test.dll" (ByVal in As String, ByVal outAs System.Text.StringBuilder)

HTH

It is doing a bit more than making standard function calls. The intent
behind my example was to show the parms.

I was not setting the character set though, and I modified my
declaration as follows:

<System.Runtime.InteropServices.DllImport("test.dl l",
CharSet:=CharSet.Ansi)_
Private Shared Sub CopyString(ByVal sIn As String, _
* * * * * * * * * * * * * * * ByVal sOut StringBuilder)
End Sub

The issue I run into is that when this function is called, I receive a
generic error as follows:

Test.vshost.exe has encountered a problem and needs to close. We are
sorry for the inconvenience.

I'm not receiving anything useful in indicating what the issue i

Well... You need to allocate the StringBuilder first.
Dim sOut As New StringBuilder (sIn.Length)

An alternative, and maybe better thinking about it, is to pass the
second parameter as an IntPtr and then use he Marshal.PtrToStringAnsi
function to get back to a managed string.

--
Tom Shelton