help on calling C functions from C# involving structures

[praveenbehara]

Hi,
I have been trying to marshal data from C# onto a C function which accepts a pointer to a structure.

The structure is as below...

=====================
struct Details
{
int ssno;
char name[50];
char hobbies[10][30];
ADDRESS addr[3];
}DETAILS;

struct Address
{
int hno;
char street[20];
}ADDRESS;

int updateDetails(DETAILS *);
=======================

But I am having problem with sending double dimensional arrays e.g: the hobbies field.
I am not aware to find a proper match to Marshal it.
Even I have given LPArray, ByValArray etc., but it doesn't work.

I am looking for a equivalent structure that I can define in C# code.
The structures that I have created in C# and that do not work
===================
[StructLayout(LayoutKind.Sequential,CharSet=CharSet .Ansi)]
public struct DETAILS
{
public int ssno;
[MarshalAs(UnmanagedType.ByValTStr,SizeConst = 50)]
public String name;
[MarshalAs(UnmanagedType.ByValArray, SizeConst=10)]
public String[] hobbies;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
public ADDRESS[] addr;
}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet .Ansi)]
public struct ADDRESS
{
public int hno;
[MarshalAs(UnmanagedType.ByValTStr,SizeConst = 20)]
public String street;
}
======================

I tried creating my own C dll and created a function to read and print the data.
The data comes fine until ssno and name.
But all other hobbies and Address details are junk characters.
Any inputs would be of great help.

[praveenbehara]

Finally I pulled this off... But I had to severely go through all the odds and possibilities to get to it.

Key:

1. When passed in structures, array of strings do not go as intended and it was creating problems, because it was sending as pointers or some other weird reason. I would be grateful, if somebody can explain that.

So, finally, I put that string in a structure and instead of array of strings, made it into a array of structures.

2. Never try to send your Int16 to C int, thinking both are 2 byte in length. Though the documentation clearly says Int32 of C# is ported to int in C, while dumping the memory, I had my own doubts and tried to tinker with it.

Ultimately, my final code looked this way... Hope this would help somebody and save their time.

Details.cpp

=========================

#include <iostream>
#include <conio>
#include <stdio>
#include <windows>

typedef struct Address
{
int hno;
char street[10];
}ADDRESS;

typedef struct Details
{
int ssno;
char name[50];
char hobbies[10][30];
ADDRESS addr[2];
}DETAILS;

extern "C" __declspec(dllexport) void WINAPI printDetails(DETAILS *d)
{
std::cout<<"Social sec no : " << d->ssno << std::endl;
std::cout<<"Name : " << d->name << std::endl;

for(int i=0;i<10;i++)
std::cout << "Hobby[" << i << "]: " << d->hobbies << std::endl;

for(int i=0;i<2;i++)
{
std::cout << "Address[" << i << "]:" << std::endl;
std::cout << "Hno : " << d->addr.hno << std::endl;
std::cout << "Street : " << d->addr.street << std::endl;
}
}

=====================



TestMarshal.cs

=====================

using System;
using System.Runtime.InteropServices;
using System.Collections.Generic;
using System.Text;
namespace MarshalProject
{
class TestMarshal
{
#region DeclareStructs
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct DETAILS
{
public int ssno;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 50)]
public String name;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 10)]
public HOBBIES[] hobbies;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
public ADDRESS[] addr;
}

[StructLayout(LayoutKind.Sequential,CharSet = CharSet.Ansi)]
public struct HOBBIES
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=30)]
public String hobby;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct ADDRESS
{
public int hno;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
public String street;
}
#endregion DeclareStructs

#region DLLFuncs
[DllImport("details.dll")]
public static extern void printDetails(ref DETAILS d);
#endregion DLLFuncs

static void Main(string[] args)
{
try
{
DETAILS d = new DETAILS();
d.ssno = 100;
d.name = new String((char)'A',50);
d.hobbies = new HOBBIES[10];

for (int i = 0; i < d.hobbies.Length; i++)
d.hobbies.hobby = "";

d.hobbies[0].hobby = new String((char)'C', 50);
d.hobbies[1].hobby = new String((char)'D', 50);
d.hobbies[2].hobby = new String((char)'E', 50);

d.addr = new ADDRESS[2];
d.addr[0].hno = 10;
d.addr[0].street = "abcd";
d.addr[1].hno = 20;
d.addr[1].street = "efgh";

printDetails(ref d);
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
}
}
}

=========================

Cheers all