using System;

using System.Text;

using System.Runtime.InteropServices;

// # Compile on Linux with:

// $ dotnet /usr/share/dotnet/sdk/5.0.103/Roslyn/bincore/csc.dll \

// -reference:/usr/share/dotnet/packs/Microsoft.NETCore.App.Ref/5.0.0/ref/net5.0/System.Runtime.dll \

// -reference:/usr/share/dotnet/packs/Microsoft.NETCore.App.Ref/5.0.0/ref/net5.0/System.Console.dll \

// -reference:/usr/share/dotnet/packs/Microsoft.NETCore.App.Ref/5.0.0/ref/net5.0/System.Runtime.InteropServices.dll \

// -out:Program.dll Program.cs

public static class Program

{

// C glibc function with variable arguments ...

// int sscanf (const char *str, const char *format, ...);

// This function reads data from "str", splits it up using "format"

// and then stores the results in the locations pointed to by the

// remaining arguments (the "...") which are variable in both number and type.

// Therefore sscanf("%d", "112", varargs ) is eqivalent to int.Parse()

// Attempt 1: Unhandled exception. System.Runtime.InteropServices.MarshalDirectiveException: Cannot marshal 'parameter #3': Signature is not Interop compatible.

// [DllImport("libc.so.6", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]

// static extern int sscanf(string str, string format, params object[] varargs);

// Attempt 2: It works!!!

// [DllImport("libc.so.6", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]

// static extern int sscanf(string str, string format,

// out int arg1, out char arg2, out int arg3, out char arg4, StringBuilder arg5);

// Attempt 3: Unhandled exception. System.InvalidProgramException: Vararg calling convention not supported.

// [DllImport("libc.so.6", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]

// static extern int sscanf(string str, string format, __arglist);

// NOTE

// The problem with __arglist is that it is painfully slow. But that is

// the official mechanism in .NET for supporting variable arguments.

// It really only exists for the purposes of supporting varargs methods via P/Invoke.

// Simplified with no vararg, and single int arg

[DllImport("libc.so.6", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]

static extern int sscanf(string str, string format, out int arg1);

public static void Main()

{

//string str = "1 + 2 = three";

//string format = "%d %c %d %c %s"; // int, char, int, char, string

// Attempt 1:

// object[] varargs = new object[5];

// int result = sscanf(str, format, varargs);

// for (int i = 0; i < result; i++)

// Console.WriteLine(varargs[i]);

// Attempt 2

// int arg1, arg3;

// char arg2, arg4;

// var arg5 = new StringBuilder(5); // need a buffer big enough to return the string

// int result = sscanf(str, format, out arg1, out arg2, out arg3, out arg4, arg5);

// Console.WriteLine("{0} {1} {2} {3} {4}", arg1, arg2, arg3, arg4, arg5);

// Attempt 3:

// int arg1=default, arg3=default;

// char arg2=default, arg4=default;

// var arg5 = new StringBuilder(5); // need a buffer big enough to return the string

// int result = sscanf(str, format, __arglist(ref arg1, ref arg2, ref arg3, ref arg4, arg5));

// Console.WriteLine("{0} {1} {2} {3} {4}", arg1, arg2, arg3, arg4, arg5);

// str = "one + 2 = 3";

// format = "%s %c %d %c %d"; // string, char, int, char, int

// result = sscanf(str, format, __arglist(arg5, out arg2, out arg1, out arg4, out arg3));

// Console.WriteLine("{0} {1} {2} {3} {4}", arg5, arg2, arg1, arg4, arg3);

// Console.ReadKey();

// This will show us (via ildasm) how to p/invoke using IL

string s = "123";

string format = "%d"; // int

int result;

int c = sscanf(s, format, out result);

Console.WriteLine("Result = {0}", result);

Console.ReadKey();

}

}