C#

public void ThisIsaReallyStupidThingToDo(string input, out int value)
{
  try
  {
    if (string.IsNullOrWhiteSpace(input))
    {
      throw new ArgumentNullException($"The value of {nameof(input)} must be set");
    }
    int.TryParse(input, out value);
  }
  catch (Exception ex)
  {
    // Log and consume the exception...
  }
}

{
  outParam= ..
}

try
{
  // No other code here!
  outParam= ...
  // more code here
}

xiecsuk wrote:

That's all I want to do; replace the old with the new value

writer.Seek(0);

const string filename = "wwwroot/Counter/Counter.txt";
using (var counterStream = new FileStream(filename, FileMode.Open, FileAccess.ReadWrite, FileShare.None))
{
    int visits;
    using (var reader = new StreamReader(counterStream))
    {
        string line = reader.ReadLine;
        int.TryParse(line, out visits);
    }
    
    visits = visits + 1;
    counterStream.Seek(0L, SeekOrigin.Begin);
    
    using (var writer = new StreamWriter(counterStream))
    {
        writer.Write(visits);
    }
}

An exception of type 'System.ObjectDisposedException' occurred in System.IO.FileSystem.dll but was not handled in user code

Additional information: Cannot access a closed file.

using (var reader = new StreamReader(counterStream, System.Text.Encoding.UTF8, true, 4096, true))

var reader = new StreamReader(counterStream);
string line = reader.ReadLine;
int.TryParse(line, out visits);
...

You have to do the following to get the saved Counter :
1.1. Open the File
1.2. Read your Value
1.3. Close the File

And you have to do the following to save the Counter :
2.1. Open the File
2.2. Write your Value
2.3. Close the File

private static int _count;
private static readonly string _fileName = @"C:\my\file\path\and.name";
private static readonly Object _sync = new Object();

public static void Increment()
{
   lock(_sync)
   {
      _count++;

      File.WriteAllText(_fileName, _count.ToString());
   }         
}

void AppStartEvent()
{
   lock(_sync)
   {
      var seed = File.ReadAllText(_fileName);
      int result = 0;
      if(int.TryParse(seed,out result))
      {      
         _count = result;
      }else{
         _count = 0;
      }
   }   
}