Re: Unions in C Sharp
- From: gmccallum <gmccallum@xxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 11 Apr 2005 06:42:01 -0700
Yes this works when only dealing with numbers, but I have been unable to find
a way to mix numbers and strings like such:
typedef struct {
int i;
char *str;
}
In this case you need to marshall the number as Explicit but the string as
Sequential. So you would think that the solution would look something like:
[ StructLayout( LayoutKind.Explicit, Size=128 )]
public struct LITERAL_1
{
[ FieldOffset( 0 )]
public int i;
}
[ StructLayout( LayoutKind.Sequential )]
public struct LITERAL_2
{
[ MarshalAs( UnmanagedType.ByValTStr, SizeConst=128 )]
public String str;
}
[StructLayout(LayoutKind.Explicit)]
public struct LITERAL
{
[FieldOffset(0)]
public LITERAL_1 iValue;
[FieldOffset(0)]
public LITERAL_2 strValue;
}
But this errors at runtime. Is there any easy way to create a union where a
string and a number could share the same starting point?
-Greg
"Chua Wen Ching" wrote:
> Hi Fritz,
>
> I totally agree with Sherif. To get you started!
>
> I have an example for you. Hope you can find it useful...
>
> C
> ---
> typedef union ChannelProtocol {
> struct {
> uint8 data2;
> uint8 data1;
> } b;
> struct {
> uint16 data12;
> } w;
> } CProtocol;
>
> C#
> ----
> [StructLayout(LayoutKind.Explicit)]
> public struct ChannelProtocol
> {
> [StructLayout(LayoutKind.Explicit)]
> public struct Sb
> {
> [FieldOffset(0)]
> public byte data2;
> [FieldOffset(1)]
> public byte data1;
> }
>
> [FieldOffset(0)]
> public Sb _Sb;
>
> [StructLayout(LayoutKind.Explicit)]
> public struct Sw
> {
> [FieldOffset(0)]
> public ushort data12;
> }
>
> [FieldOffset(0)]
> public Sw _Sw;
> }
>
> Cheers.
>
> "Sherif ElMetainy" wrote:
>
> > Hello
> >
> > Use StructLayout.Explicit with FieldOffsetAttribute. See documentation of
> > both attributes in MSDN
> >
> > Best regards,
> > Sherif
> >
> > "Fritz" <fritz@xxxxxxxxxxxxxxxx> wrote in message
> > news:#wfkIpUFFHA.1348@xxxxxxxxxxxxxxxxxxxxxxx
> > > Is is possible to create a C style union in C Sharp? I'm trying to call
> > > functions in an unmanaged DLL that has a struct with unions in it as a
> > > function parameter. I've looked at the "StructLayout" attribute and the
> > > unmanaged code examples but I don't see anything about unions.
> > >
> > > Regards,
> > >
> > > Fritz
> > >
> > >
> >
> >
> >
.
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