C#

using System;
using System.Runtime.InteropServices;
using System.Globalization;

namespace CsharpManaged
{
    class Program
    {
        public delegate void CallbackDelegate(
            IntPtr INBuffer, UInt32 INBufferLength,
            IntPtr OUTBuffer, UInt32 OUTBufferLength);

        [DllImport("CppDLLUnmanaged.dll", CallingConvention = CallingConvention.StdCall)]
        private static extern void SetCallBackPointer(CallbackDelegate DelegatePassedToDLL);

        [DllImport("CppDLLUnmanaged.dll", CallingConvention = CallingConvention.StdCall)]
        private static extern void InvokeCallBack();

        static void Main(string[] args)
        {
            SetCallBackPointer(new CallbackDelegate(CallbackFunction));
            InvokeCallBack();

            Console.ReadLine();
        }

        private static void CallbackFunction(
            IntPtr INBuffer, UInt32 INBufferLength,
            IntPtr OUTBuffer, UInt32 OUTBufferLength)
        {
            // For the example, we'll copy the IN buffer into the OUT buffer.
            // We'll also show it on screen
            Console.WriteLine("C#:");
            unsafe
            {
                Byte* INptr = (Byte*)INBuffer.ToPointer();
                Byte* OUTptr = (Byte*)OUTBuffer.ToPointer();
                // Truncating the biggest buffer (we don't want to write into non
                // allocated memory).
                UInt32 length =
                    (INBufferLength < OUTBufferLength) ? INBufferLength : OUTBufferLength;
                for (UInt32 i = 0; i < length; ++i)
                {
                    Console.WriteLine(Convert.ToString(*INptr));
                    *OUTptr = *INptr;
                    ++INptr;
                    ++OUTptr;
                }
            }
            Console.WriteLine();
        }
    }
}

#include <iostream>
using namespace std;

// This is the prototype of the callback function
typedef void __stdcall CALL_BACK_FUNCTION(char* INBuffer, unsigned long INBufferLength,
										  char* OUTBuffer, unsigned long OUTBufferLength);

// This is only function that actually has to be exported. The caller will pass a pointer
// to the function it wants to use as callback.
CALL_BACK_FUNCTION *pFunction;
__declspec(dllexport) void __stdcall SetCallBackPointer(CALL_BACK_FUNCTION* FnAddress)
{
	pFunction = FnAddress;
}

// For the example, this is the function that will activate the
// callback. It won't exist in practice.
__declspec(dllexport) void __stdcall InvokeCallBack()
{
	// Allocating memory for the buffers
	char* INBuffer, * OUTBuffer;
	unsigned long INBufferLength, OUTBufferLength;

	INBufferLength = 10;
	OUTBufferLength = 15;

	INBuffer  = new char[INBufferLength];
	OUTBuffer = new char[OUTBufferLength];
	////////////////////////////////////////////////////////////
	
	// Filling the buffer with binary data, just for the example.
	for(int i = 0; i < INBufferLength; ++i)
	{
		INBuffer[i] = i;
	}
	////////////////////////////////////////////////////////////

	// Making the callback
	pFunction(INBuffer,INBufferLength,OUTBuffer,OUTBufferLength);
	////////////////////////////////////////////////////////////

	// Showing the return buffer contents, to show that the
	// transfer took place as expected.
	cout << "C++" << endl;
	for(unsigned long i = 0; i < OUTBufferLength; ++i)
	{
		char digit;
		itoa(OUTBuffer[i],&digit,10);
		cout << digit << endl;
	}
	////////////////////////////////////////////////////////////

	// Freeing allocated memory
	delete [] INBuffer;
	delete [] OUTBuffer;
	////////////////////////////////////////////////////////////
}

FileStream fs = new FileStream("message.txt", FileMode.Create, FileAccess.Write, FileShare.None, 8192, false);
fs.Write(textValue, 0, textValue.Length);
fs.Close();
fs = null;

troubled one wrote:

for example, when someone enters "hello" in textbox1 as "message.txt", and clicks send button, the streamwriter will save the file into a notepad as "message.txt"

troubled one wrote:

but is it possible to store that notepad permanently such that if the user clicks the send button another time with a different content like "goodbye", the streamwriter will save the file into a different notepad like "message2.txt" and the content will be "goodbye" ?

N a v a n e e t h wrote:

StreamWriter won't be able to create a file.

Giorgi Dalakishvili wrote:

StreamWriter creates a new file if it doesn't exist.