C# Signature:

[DllImport("kernel32.dll", SetLastError=true)]
static extern IntPtr CreateToolhelp32Snapshot(SnapshotFlags dwFlags, uint th32ProcessID);

VB.NET Signature:

<DllImport("kernel32.dll", SetLastError:=True)> _
Private Shared Function CreateToolhelp32Snapshot(ByVal dwFlags As SnapshotFlags, ByVal th32ProcessID As UInteger) As IntPtr
End Function

User-Defined Types:

[Flags]
public enum SnapshotFlags : uint
{
    HeapList = 0x00000001,
    Process  = 0x00000002,
    Thread   = 0x00000004,
    Module   = 0x00000008,
    Module32 = 0x00000010,
    Inherit  = 0x80000000,
    All      = 0x0000001F
}

Notes:

None.

Tips & Tricks:

Please add some!

Sample Code:

using System;
using System.Runtime.InteropServices;
using System.Diagnostics;
static class myProcessEx
{  
    //inner enum used only internally
    [Flags]
    private enum SnapshotFlags : uint
    {
    HeapList = 0x00000001,
    Process = 0x00000002,
    Thread = 0x00000004,
    Module = 0x00000008,
    Module32 = 0x00000010,
    Inherit = 0x80000000,
    All = 0x0000001F
    }
    //inner struct used only internally
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    private struct PROCESSENTRY32
    {
    const int MAX_PATH = 260;
    internal UInt32 dwSize;
    internal UInt32 cntUsage;
    internal UInt32 th32ProcessID;
    internal IntPtr th32DefaultHeapID;
    internal UInt32 th32ModuleID;
    internal UInt32 cntThreads;
    internal UInt32 th32ParentProcessID;
    internal Int32 pcPriClassBase;
    internal UInt32 dwFlags;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = MAX_PATH)]
    internal string szExeFile;
    }

    [DllImport("kernel32", SetLastError = true, CharSet = System.Runtime.InteropServices.CharSet.Auto)]
    static extern IntPtr CreateToolhelp32Snapshot([In]UInt32 dwFlags, [In]UInt32 th32ProcessID);

    [DllImport("kernel32", SetLastError = true, CharSet = System.Runtime.InteropServices.CharSet.Auto)]
    static extern bool Process32First([In]IntPtr hSnapshot, ref PROCESSENTRY32 lppe);

    [DllImport("kernel32", SetLastError = true, CharSet = System.Runtime.InteropServices.CharSet.Auto)]
    static extern bool Process32Next([In]IntPtr hSnapshot, ref PROCESSENTRY32 lppe);

    // get the parent process given a pid
    public static Process GetParentProcess(int pid)
    {

    Process parentProc = null;
    try
    {
        PROCESSENTRY32 procEntry = new PROCESSENTRY32();
        procEntry.dwSize = (UInt32)Marshal.SizeOf(typeof(PROCESSENTRY32));
        IntPtr handleToSnapshot = CreateToolhelp32Snapshot((uint)SnapshotFlags.Process, 0);
        if (Process32First(handleToSnapshot, ref procEntry))
        {
        do
        {
            if (pid == procEntry.th32ProcessID)
            {
            parentProc = Process.GetProcessById((int)procEntry.th32ParentProcessID);
            break;

            }
        } while (Process32Next(handleToSnapshot, ref procEntry));
        }
        else
        {
        throw new ApplicationException(string.Format("Failed with win32 error code {0}", Marshal.GetLastWin32Error()));
        }
    }
    catch (Exception ex)
    {
        throw new ApplicationException("Can't get the process.", ex);
    }
    return parentProc;
    }

    // get the specific parent process
    public static Process CurrentParentProcess
    {
    get
    {
        return GetParentProcess(Process.GetCurrentProcess().Id);
    }
    }

    static void Main()
    {
    Process pr = CurrentParentProcess;

    Console.WriteLine("Parent Proc. ID: {0}, Parent Proc. name: {1}", pr.Id, pr.ProcessName);
    }
}

See also:

PROCESSENTRY32, Process32First, Process32Next

Alternative Managed API:

Do you know one? Please contribute it!