Simple marshalling hello world with nested struct.

hello.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include "hello.h"

static const char* get_field(char *line, int num)
{
	const char *tok;
	for (tok = strtok(line, ","); tok && *tok; tok = strtok(NULL, ",\n")) {
		if (!--num)
			return tok;
	}
	return NULL;
}

static int parse_human(char *line, struct human *human)
{
		char *tmp = strdup(line);
		const char *f;

		printf("&human=%ld\n", human);
		printf("&human->contact=%ld\n", human->contact);
		f = get_field(tmp, 1);
		printf("field 1='%s'\n", f);
		memset(human->first, 0, sizeof(human->first));
		strcpy(human->first, f);
		free(tmp);
		tmp = strdup(line);
		f = get_field(tmp, 2);
		printf("field 2='%s'\n", f);
		memset(human->last, 0, sizeof(human->last));
		strcpy(human->last, f);
		free(tmp);
		tmp = strdup(line);
		f = get_field(tmp, 3);
		printf("field 3='%s'\n", f);
		memset(human->contact->cell, 0, sizeof(human->contact->cell));
		strcpy(human->contact->cell, f);
		free(tmp);
		tmp = strdup(line);
		f = get_field(tmp, 4);
		printf("field 4='%s'\n", f);
		memset(human->contact->home, 0, sizeof(human->contact->home));
		strcpy(human->contact->home, f);
		free(tmp);

		return 0;
}

HELLOAPI int HELLOCALL say_hello(struct human *person)
{
	printf("Hello, %s %s\n", person->first, person->last);
	if (person->contact && person->contact->cell)
		printf("\tcell: %s\n", person->contact->cell);
	if (person->contact && person->contact->home)
		printf("\thome: %s\n", person->contact->home);
	return 0;
}

HELLOAPI int HELLOCALL import_csv(char *path, struct human *person)
{
	int res;
	FILE *csv;
	char line[1024];

	if (person == NULL) {
		return ENOMEM;
	}

	printf("parsing: '%s'\n", path);
	csv = fopen(path, "r");
	if (csv == NULL) {
		return errno;
	}

	fgets(line, 1024, csv);
	printf("parsing: '%s'\n", line);
	res = parse_human(line, person);
	if (res != 0) {
		return res;
	}

	fclose(csv);

	return 0;
}

hello.h

#ifndef ___HELLO_H
#define ___HELLO_H

#ifdef _WIN32
  //#ifdef par_EXPORTS
    #define HELLOAPI __declspec(dllexport)
  //#else
  //  #define HELLOAPI __declspec(dllimport)
  //#endif
  #define HELLOCALL __cdecl
#else
  #define HELLOAPI
  #define HELLOCALL
#endif

#ifdef __cplusplus
extern "C" {
#endif

struct contact_info {
	char cell[32];
	char home[32];
};

struct human {
	char first[32];
	char last[32];
	struct contact_info *contact;
};

HELLOAPI int HELLOCALL say_hello(struct human *person);
HELLOAPI int HELLOCALL import_csv(char *path, struct human *person);

#ifdef __cplusplus
}
#endif

#endif /* ___HELLO_H */

HelloLibrary.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace HelloApp
{
    class HelloLibrary
    {
        [StructLayout(LayoutKind.Sequential)]
        public struct contact_info
        {
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
            public String cell;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
            public String home;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct human
        {
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
            public String first;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
            public String last;
            public IntPtr contact;
        }

        [DllImport("HelloLibrary.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern int say_hello(ref human person);

        [DllImport("HelloLibrary.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern int import_csv([MarshalAs(UnmanagedType.LPStr)]String path,
            ref human person);
    }
}

people.csv

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace HelloApp
{
    class Program
    {
        static void Main(string[] args)
        {
            if (args.Length < 1)
            {
                Console.WriteLine("Specify a CSV file.");
                Environment.Exit(1);
            }

            //HelloLibrary.human person = new HelloLibrary.human();
            //person.first = "Joe";
            //person.last = "Schmoe";
            //HelloLibrary.contact_info info = new HelloLibrary.contact_info();
            //info.cell = "1234567890";
            //info.home = "";
            //IntPtr ptr1 = Marshal.AllocHGlobal(Marshal.SizeOf(info));
            //Marshal.StructureToPtr(info, ptr1, true);
            //person.info = ptr1;

            //HelloLibrary.say_hello(ref person);


            HelloLibrary.human human = new HelloLibrary.human();
            human.contact = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(HelloLibrary.contact_info)));
            //human.contact = Marshal.AllocCoTaskMem(Marshal.SizeOf(typeof(HelloLibrary.contact_info)));
            //HelloLibrary.contact_info contact = new HelloLibrary.contact_info();
            //IntPtr hptr = Marshal.AllocHGlobal(Marshal.SizeOf(human));
            //IntPtr ptr = Marshal.AllocHGlobal(Marshal.SizeOf(contact));
            //IntPtr hptr = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(HelloLibrary.human)));
            //IntPtr iptr = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(HelloLibrary.contact_info)));
            //HelloLibrary.human human = (HelloLibrary.human)Marshal.PtrToStructure(
            //    hptr, typeof(HelloLibrary.human));
            HelloLibrary.contact_info contact = (HelloLibrary.contact_info)Marshal.PtrToStructure(
                human.contact, typeof(HelloLibrary.contact_info));
            //Marshal.PtrToStructure(hptr, human);
            //Marshal.PtrToStructure(iptr, contact);
            //human.contact = iptr;
            //Marshal.StructureToPtr(contact, human.contact, true);
            Console.WriteLine("&human.contact={0}", human.contact);

            //HelloLibrary.import_csv(args[0], ref hptr);
            HelloLibrary.import_csv(args[0], ref human);

            Console.WriteLine("first:'{0}'", human.first);
            Console.WriteLine("last:'{0}'", human.last);
            Console.WriteLine("cell:'{0}'", contact.cell);
            Console.WriteLine("home:'{0}'", contact.home);

            Console.Read();
        }
    }
}