Re: Little Problem

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From: Angel J. Hernández M (angeljesus14_at_hotmail.com)
Date: 09/13/04 

Date: Mon, 13 Sep 2004 16:57:29 -0400

Hi there... That's not the problem...

I've got a code written in C# and works fine but I call a lot of API
functions so I decided to write the low-level stuff in C++. My problem is
(not about __pin cuz I already try that). I have a struct which is
responsible for storing packet's IP Header. It's defined like this...

            [StructLayout(LayoutKind::Explicit)]
             __value struct IPHeader {
                 [FieldOffset(0)] Byte verlen; // IP Version & IP Header
length
                 [FieldOffset(1)] Byte tos; // Type of service
                 [FieldOffset(2)] UInt16 length; // Packet's total length
                 [FieldOffset(4)] UInt16 id; // Unique identifier
                 [FieldOffset(6)] UInt16 offset; // Flags & Offset
                 [FieldOffset(8)] Byte ttl; // Time To Live
                 [FieldOffset(9)] Byte protocol; // Protocol (TCP, UDP, any
other)
                 [FieldOffset(10)] UInt16 checksum; // IP Header checksum
                 [FieldOffset(12)] Int64 source; // Source address
                 [FieldOffset(16)] Int64 destination; // Destination address
                 };

What I want to do (like I did in C# code) is... Fill all of the structs
fields by using a pointer... In C# I have this code

 protected virtual unsafe object[] ParseIPHeader(byte[] packet, int length)
{
    short src_port = 0, dst_port = 0;
    object[] retval = new object[6];

    fixed(byte* packetdata = packet) {
     CCommon.IPHeader* ipheader = (CCommon.IPHeader*) packetdata;
    // Rest of code goes here...
}

As you can see I fix my pointer and it's initialized with packet's address.
In C# I don't have to use the & operator for an operation like the one shown
above. My problem is that... I want to get the same result in C++.

Object* CRawSocket::ParseIPHeader(Byte packet[], int length)[] {
     short src_port = 0, dst_port = 0;
     System::Text::StringBuilder *src_address, *dst_address;
     Object *retval[] = new Object*[6];
     src_address = new System::Text::StringBuilder();
     dst_address = new System::Text::StringBuilder();

     Byte *packeddata = __try_cast< Byte *>(&packet[0]) ;
     CCommon::IPHeader *ipheader = (CCommon::IPHeader *) &packeddata;
     // Rest of code goes here...
}

I open two instances of VS Debugger (C# & C++ projects). The ipheader points
to packeddata which in turn points to the first element of the array
packet. This works perfectly in C# but it doesn't seem to work in C++. When
I compare both structures (C# & C++) the information contaned in them is
totally different when the data received from the socket is the same.

TIA

"Ben Schwehn" <b.schwehn@gmx.net> escribió en el mensaje
news:%23PzpuCdmEHA.744@TK2MSFTNGP10.phx.gbl...
>
> > fixed(byte* packetdata = &packet) // wrong!
> >
> > but in the C++ world I need to pass the address
> >
> > I've tried this...
>
> I'm not entirly sure what you're trying to do but instead of c#'s fixed
> what you'll probably want to do is use __pin something like
>
> int __pin* p = &packet[0];
>
> to get the address of packet and also pin the entire array
>
> hth
> --
> Ben
> http://bschwehn.de

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