How do I send ctrl+c to a process in c#?

I've actually just figured out the answer. Thank you both for your answers, but it turns out that all i had to do was this:

p.StandardInput.Close()

which causes the program I've spawned to finish reading from stdin and output what i need.

@alonl: The user is attempting to wrap a command-line program. Command-line programs don't have message pumps unless they are specifically created, and even if that was the case, Ctrl+C doesn't have the same semantics in a Windows-environment application (copy, by default) as it does in a command-line environment (Break).

I threw this together. CtrlCClient.exe simply calls Console.ReadLine() and waits:

static void Main(string[] args)
{
    ProcessStartInfo psi = new ProcessStartInfo("CtrlCClient.exe");
    psi.RedirectStandardInput = true;
    psi.RedirectStandardOutput = true;
    psi.RedirectStandardError = true;
    psi.UseShellExecute = false;
    Process proc = Process.Start(psi);
    Console.WriteLine("{0} is active: {1}", proc.Id, !proc.HasExited);
    proc.StandardInput.WriteLine("\x3");
    Console.WriteLine(proc.StandardOutput.ReadToEnd());
    Console.WriteLine("{0} is active: {1}", proc.Id, !proc.HasExited);
    Console.ReadLine();
}

My output seems to do what you want:

4080 is active: True
4080 is active: False

Hope that helps!

(To clarify: \x3 is the hex escape sequence for the hex character 3, which is Ctrl+C. It's not just a magic number. ;) )

FWIW, in my case, what I wanted is, from a console process, create a child console process (ffmpeg.exe for that matter) and support clean CTRL-C handling in my process and in the child process (ffmpreg exits normally when CTRL-C is pressed which is a nice feature I wanted to keep working)

None of the solution I found here were working, so I just interop'd Windows' CreateProcess function and it just works w/o any effort, CTRL-C is automatically received by the child app and by the parent app, input and output streams are shared, etc. I was not able to reproduce that kind of code using the standard .NET Process class:

    static void RunFFMpeg(string arguments)
    {
        var startup = new STARTUPINFO();
        startup.cb = Marshal.SizeOf<STARTUPINFO>();
        if (!CreateProcess(null, "ffmpeg.exe " + arguments, IntPtr.Zero, IntPtr.Zero, false, 0, IntPtr.Zero, null, ref startup, out var info))
            throw new Win32Exception(Marshal.GetLastWin32Error());

        CloseHandle(info.hProcess);
        CloseHandle(info.hThread);

        var process = Process.GetProcessById(info.dwProcessId);
        Console.CancelKeyPress += (s, e) =>
        {
            process.WaitForExit();
            Console.WriteLine("Abort.");
            // end of program is here
        };

        process.WaitForExit();
        Console.WriteLine("Exit.");
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct PROCESS_INFORMATION
    {
        public IntPtr hProcess;
        public IntPtr hThread;
        public int dwProcessId;
        public int dwThreadId;
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    private struct STARTUPINFO
    {
        public int cb;
        public string lpReserved;
        public string lpDesktop;
        public string lpTitle;
        public int dwX;
        public int dwY;
        public int dwXSize;
        public int dwYSize;
        public int dwXCountChars;
        public int dwYCountChars;
        public int dwFillAttribute;
        public int dwFlags;
        public short wShowWindow;
        public short cbReserved2;
        public IntPtr lpReserved2;
        public IntPtr hStdInput;
        public IntPtr hStdOutput;
        public IntPtr hStdError;
    }

    [DllImport("kernel32")]
    private static extern bool CloseHandle(IntPtr hObject);

    [DllImport("kernel32", SetLastError = true, CharSet = CharSet.Unicode)]
    private static extern bool CreateProcess(
       string lpApplicationName,
       string lpCommandLine,
       IntPtr lpProcessAttributes,
       IntPtr lpThreadAttributes,
       bool bInheritHandles,
       int dwCreationFlags,
       IntPtr lpEnvironment,
       string lpCurrentDirectory,
       ref STARTUPINFO lpStartupInfo,
       out PROCESS_INFORMATION lpProcessInformation);

Try actually sending the Key Combination Ctrl+C, instead of directly terminating the process:

 [DllImport("user32.dll")]
        public static extern int SendMessage(
              int hWnd,      // handle to destination window
              uint Msg,       // message
              long wParam,  // first message parameter
              long lParam   // second message parameter
              );

Look it up on the MSDN, you should find what you need there in order to send the Ctrl+Key combination... I know that the message you need for sending Alt+Key is WM_SYSTEMKEYDOWN and WM_SYSTEMKEYUP, can't tell you about Ctrl...