Passing values from C# from/to a C++ dll

[Bob Yang]

Hi, I have this in C++ and I like to call it from c# to get the value
but I fail. it will be good if you can give me some information. I
tried it in VB.net it works but I use almost the same way as VB in C#
but it doens't work.

c++: (csp2.dll)
NoMangle long DLL_IMPORT_EXPO RT csp2TimeStamp2S tr(unsigned char
*Stamp, char *value, long nMaxLength);


VB.net: (this works correctly)

Declare Function csp2TimeStamp2S tr Lib "csp2.dll" (ByRef Stamp As
Byte, ByVal value As String, ByVal nMaxLength As Integer) As Integer

Dim nRC As Integer
Dim arrbyteBarcode( 99) As Byte '100 elements
Dim nBytesRead As Integer
Dim bstrTmp As New VB6.FixedLength String(50)

nBytesRead = csp2GetPacket(a rrbyteBarcode(0 ), i, 100)

nRC = csp2TimeStamp2S tr(arrbyteBarco de(nBytesRead - 4), bstrTmp.Value,
Len(bstrTmp.Val ue))
TextBox1.text= VB.Left(bstrTmp .Value, 20)


C#: (this doesn't work :( )

[System.Runtime. InteropServices .DllImport("csp 2.DLL")] static extern
int csp2TimeStamp2S tr(byte value, string Stamp, int nMaxLength);

int nRC, nBytesRead;
byte[] arrbyteBarcode= new byte[100];
FixedLengthStri ng bstrTmp = new FixedLengthStri ng(50);

nBytesRead = csp2GetPacket(a rrbyteBarcode[0], i, 100);
bstrTmp=" ";

nRC = csp2TimeStamp2S tr(arrbyteBarco de[nBytesRead-4],
bstrTmp.Value, bstrTmp.Value.L ength);
TextBox1.text= bstrTmp.Value.t oString();

[Ben Voigt [C++ MVP]]

"Bob Yang" <bo******@gmail .comwrote in message
news:11******** **************@ 57g2000hsv.goog legroups.com...

thank you! great information.

2. if I have a c++ as (unsigned char[] ca1, char[] ca2), how can I
call it correctly in c#? is it equal to (byte[] ca1, byte[] ca2)?

More precisely ca2 would be sbyte[], but byte[] should also work.

Moreover, ca1 and ca2 are only passing IN the the value and c++ cannot
change the value because it is not a pointer in c++?

The DLL cannot change the caller's variable to a different array. It can
however change the content of the array passed in the call, which is shared
with the caller.

[rednael]

Please read the following article:
http://blog.rednael.com/2008/08/29/M...DLLsInNET.aspx

It's an in depth article about marshalling between native code and managed code. It shows which types are interoperable, how to import a DLL, how to pass strings, how to pass structures and how to de-reference pointers.

Code examples in C# are included.