[RESOLVED] Question about C structure

[bmahler]

Ok, to start... I am very unfamiliar with c and c++. I have a simple app written in C and I am trying to convert it to vb.net. I am just wondering about a structure that is in the file. this is the structure.

struct Packet {
	int size;
	int (*realFunc)(void *, void *, void *, unsigned char *, int, void *);
	unsigned int repeat;
	unsigned char buf[2048];
};

I can convert it for the most part, but that function (if that is what it is) confuses me.

This is what I have so far

    Private Structure Packet
        Dim size As Integer

        Public Function realFunc(ByVal val1 As Object, ByVal val2 As Object, _
            ByVal val3 As Object, ByVal SomeByte As Byte, ByVal Size As Integer, _
            ByVal val4 As Object) As Integer

            'I defined them as just objects for lack 
            'of an understanding of what they are
        End Function

        Dim Repeat As UInt32
        Dim buf() As Byte
    End Structure

What I am wondering about is the realFunc variable. Is this a function within a structure? also what does void * mean. I was under the assumption tha void was similar to declaring a sub in vb so, this really confuses me. Thanks to anyone that can help

B

[Harsh Gupta]

If I remember correctly, that is a pointer to a function realFunc accepting those parameters.

void* is a void pointer, which means that it can accept any type of pointer as a parameter. Example you can pass an int*, or float* or char* or a Packet* (yes, pointer of your structure) as first parameter.

Again said, I could be wrong. Need to brush up everything now!!!

[chemicalNova]

Yes, that is a pointer to a function, and yes, void pointers can point to an object of any type.

VB6 had the option of an "Any" type.. I'm not sure if .NET does.. give it a shot? (Dim variable As Any).

Are you just copying the data type? Or is this type actually going to be sent into your program from another source? If the latter, forget about using VB. Theres no way to overcome that obstacle.

If you're just copying the type, then the best you'll get is writing your own function for "realFunc" that always accepts the same parameters (not void objects.. which may not be available in VB.NET).

chem

[bmahler]

Ya, any is not allowed in .net. I am just trying to rewrite a simple C console app in .net and that structure was giving me a headache. Thanks for your help guys.

[wossname]

If you need to convert this:

int (*realFunc)(void *, void *, void *, unsigned char *, int, void *);

Then it might be worth investigating delegates. As for the void* arguments, you can call in IntPtr objects. All depemds how accurately you want to simulate the original functionality.

[bmahler]

well, I decided against rewriting it and instead took the C console app I had and just made a dll out of the code. Thanks again for your help.

[David Anton]

Just in case anyone's interested, here the equivalent VB code (via C++ to VB Converter):

Public Class Packet
	Public size As Integer
	Public Delegate Function realFuncDelegate(ByVal UnnamedParameter1 As IntPtr, ByVal UnnamedParameter2 As IntPtr, ByVal UnnamedParameter3 As IntPtr, ByVal UnnamedParameter4 As Byte, ByVal UnnamedParameter5 As Integer, ByVal UnnamedParameter6 As IntPtr) As Integer
	Public realFunc As realFuncDelegate
	Public repeat As UInteger
	Public buf As Byte() = New Byte(2047){}
End Class

A couple of notes:
1. The C++ struct equates to a VB Class, not a Structure. (The C++ struct is nearly identical to the C++ class, except the default access is public).
2. Array size in VB is set by specifying upper bound, not length.