Using File.AppendAllText leads to the error "The process cannot access the file is already in use"

Question

I am writing a simple program for keyloggers (for non-malicious purposes).

Note: This is with a .net 4.0 client profile.

Whenever I run the program, I get this error:

The process cannot access the file 'C:\Users\.. ..\bin\Debug\log.log' because it is being used by another process. 

Here is my main code:

 using System; using System.Collections.Generic; using System.Drawing; using System.Windows.Forms; using System.ComponentModel; using System.IO; using System.Text; namespace Logger { public partial class MainForm : Form { public string cWin = null; public static string nl = Environment.NewLine; public MainForm() { InitializeComponent(); } public static DialogResult AskOverwrite() { DialogResult result = MessageBox.Show("Log already exists. Overwrite?", "Overwrite?", MessageBoxButtons.YesNo, MessageBoxIcon.Question); return result; } private void MainForm_Resize(object sender, EventArgs e) { if (FormWindowState.Minimized == this.WindowState) { systray.Visible = true; this.Hide(); } else if (FormWindowState.Normal == this.WindowState) { systray.Visible = false; } } private void SystrayMouse_DoubleClick(object sender, MouseEventArgs e) { this.Show(); this.WindowState = FormWindowState.Normal; } private void HookManager_KeyPress(object sender, KeyPressEventArgs e) { if (Program.run) { output.AppendText(string.Format(e.KeyChar.ToString())); File.AppendAllText(Program.file, e.KeyChar.ToString()); } } private void Start_Click(object sender, EventArgs e) { if (!Program.run) { if (File.Exists(Program.file)) { if (AskOverwrite() == DialogResult.Yes) { File.Create(Program.file); } } Program.run = true; output.AppendText(string.Format("Logging started - {1}{0}", nl, System.DateTime.Now)); File.AppendAllText(Program.file, string.Format("Logging started - {1}{0}", nl, System.DateTime.Now)); } else { output.AppendText(string.Format("Logging already started!{0}", nl)); } } private void Stop_Click(object sender, EventArgs e) { if (Program.run) { Program.run = false; output.AppendText(string.Format("{0}Logging stopped - {1}{0}", nl, System.DateTime.Now)); File.AppendAllText(Program.file, string.Format("{0}Logging stopped - {1}{0}", nl, System.DateTime.Now)); } else { output.AppendText(string.Format("Logging already stopped!{0}", nl)); } } private void getWindowTimer_Tick(object sender, EventArgs e) { if (cWin != CurrentWindow.GetActiveWindow() &&Program.run) { cWin = CurrentWindow.GetActiveWindow(); if (cWin != null) { output.AppendText(string.Format("{0}Window - {1}{0}", nl, cWin)); File.AppendAllText(Program.file, string.Format("{0}Window - {1}{0}", nl, cWin)); } } } } } 

Why is this happening? This was perfect when I used this statement to write to a file:

 using (StreamWriter sr = new StreamWriter(Program.file)) { sr.Write(string.Format("texthere"); } 

But it stopped working when I switched to simple use:

 File.AppendAllText(Program.file, string.Format("texthere"); 

Answer 1

I see

  File.Create(Program.file); 

which is not necessary and probably a direct problem here.

It not only creates an empty file, but also opens and returns a FileStream object that you don't close anywhere. An open FileStream cannot be split, so it throws an AppendAllText () error.

Just delete this line, AppendAllText() includes the logic in the create file if it does not already exist