How To List Running Processes

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Article ID: 187913 - View products that this article applies to.
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This article illustrates how you can list the processes that are currently running on a computer. The approach is different for Windows 95/98 and Windows NT; this article illustrates both solutions.


This situation requires that you first test to see which version of Windows is in use. Once that determination is made, the correct code can then be run to examine and list the current processes. On Windows NT, requests for information on some system processes may be denied for security or other related reasons. The approach taken in this article will ignore any process that cannot be accessed.

PSAPI.DLL is the library used to gather process information on Windows NT and must reside in the \SYSTEM32 directory. There are two versions of this file, 3.51 and 4.0. Either version will work for this example, but using the most recent version is recommended. If you have installed the Windows NT 4.0 Resource Kit or the Windows NT 4.0 SDK, this file will be present on your computer. The 4.0 version of the file is available on the Visual Studio Visual C++ CD-ROM in the following directory:

The 3.51 version of the file is available on the Visual Studio Visual Basic CD-ROM in the directory:

Step-by-Step Example

  1. Create a new Standard Exe project in Visual Basic. Form1 is created by default.
  2. Add a CommandButton to Form1.
  3. Add a ListBox to Form1.
  4. Copy the following code to Form1:
          Option Explicit
          Private Sub Command1_Click()
          Select Case getVersion()
          Case 1 'Windows 95/98
             Dim f As Long, sname As String
             Dim hSnap As Long, proc As PROCESSENTRY32
             hSnap = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0)
             If hSnap = hNull Then Exit Sub
             proc.dwSize = Len(proc)
             ' Iterate through the processes
             f = Process32First(hSnap, proc)
             Do While f
               sname = StrZToStr(proc.szExeFile)
               List1.AddItem sname
               f = Process32Next(hSnap, proc)
          Case 2 'Windows NT
             Dim cb As Long
             Dim cbNeeded As Long
             Dim NumElements As Long
             Dim ProcessIDs() As Long
             Dim cbNeeded2 As Long
             Dim NumElements2 As Long
             Dim Modules(1 To 200) As Long
             Dim lRet As Long
             Dim ModuleName As String
             Dim nSize As Long
             Dim hProcess As Long
             Dim i As Long
             'Get the array containing the process id's for each process object
             cb = 8
             cbNeeded = 96
             Do While cb <= cbNeeded
                cb = cb * 2
                ReDim ProcessIDs(cb / 4) As Long
                lRet = EnumProcesses(ProcessIDs(1), cb, cbNeeded)
             NumElements = cbNeeded / 4
             For i = 1 To NumElements
                'Get a handle to the Process
                hProcess = OpenProcess(PROCESS_QUERY_INFORMATION _
                   Or PROCESS_VM_READ, 0, ProcessIDs(i))
                'Got a Process handle
                If hProcess <> 0 Then
                    'Get an array of the module handles for the specified
                    lRet = EnumProcessModules(hProcess, Modules(1), 200, _
                    'If the Module Array is retrieved, Get the ModuleFileName
                    If lRet <> 0 Then
                       ModuleName = Space(MAX_PATH)
                       nSize = 500
                       lRet = GetModuleFileNameExA(hProcess, Modules(1), _
                                       ModuleName, nSize)
                       List1.AddItem Left(ModuleName, lRet)
                    End If
                End If
              'Close the handle to the process
             lRet = CloseHandle(hProcess)
          End Select
          End Sub
  5. Add a Standard Module to the Project. Module1 is created.
  6. Paste the following code into Module1.
          Public Declare Function Process32First Lib "kernel32" ( _
             ByVal hSnapshot As Long, lppe As PROCESSENTRY32) As Long
          Public Declare Function Process32Next Lib "kernel32" ( _
             ByVal hSnapshot As Long, lppe As PROCESSENTRY32) As Long
          Public Declare Function CloseHandle Lib "Kernel32.dll" _
             (ByVal Handle As Long) As Long
          Public Declare Function OpenProcess Lib "Kernel32.dll" _
            (ByVal dwDesiredAccessas As Long, ByVal bInheritHandle As Long, _
                ByVal dwProcId As Long) As Long
          Public Declare Function EnumProcesses Lib "psapi.dll" _
             (ByRef lpidProcess As Long, ByVal cb As Long, _
                ByRef cbNeeded As Long) As Long
          Public Declare Function GetModuleFileNameExA Lib "psapi.dll" _
             (ByVal hProcess As Long, ByVal hModule As Long, _
                ByVal ModuleName As String, ByVal nSize As Long) As Long
          Public Declare Function EnumProcessModules Lib "psapi.dll" _
             (ByVal hProcess As Long, ByRef lphModule As Long, _
                ByVal cb As Long, ByRef cbNeeded As Long) As Long
          Public Declare Function CreateToolhelp32Snapshot Lib "kernel32" ( _
             ByVal dwFlags As Long, ByVal th32ProcessID As Long) As Long
          Public Declare Function GetVersionExA Lib "kernel32" _
             (lpVersionInformation As OSVERSIONINFO) As Integer
          Public Type PROCESSENTRY32
             dwSize As Long
             cntUsage As Long
             th32ProcessID As Long           ' This process
             th32DefaultHeapID As Long
             th32ModuleID As Long            ' Associated exe
             cntThreads As Long
             th32ParentProcessID As Long     ' This process's parent process
             pcPriClassBase As Long          ' Base priority of process threads
             dwFlags As Long
             szExeFile As String * 260       ' MAX_PATH
          End Type
          Public Type OSVERSIONINFO
             dwOSVersionInfoSize As Long
             dwMajorVersion As Long
             dwMinorVersion As Long
             dwBuildNumber As Long
             dwPlatformId As Long           '1 = Windows 95.
                                            '2 = Windows NT
             szCSDVersion As String * 128
          End Type
          Public Const PROCESS_QUERY_INFORMATION = 1024
          Public Const PROCESS_VM_READ = 16
          Public Const MAX_PATH = 260
          Public Const STANDARD_RIGHTS_REQUIRED = &HF0000
          Public Const SYNCHRONIZE = &H100000
          Public Const PROCESS_ALL_ACCESS = &H1F0FFF
          Public Const TH32CS_SNAPPROCESS = &H2&
          Public Const hNull = 0
          Function StrZToStr(s As String) As String
             StrZToStr = Left$(s, Len(s) - 1)
          End Function
          Public Function getVersion() As Long
             Dim osinfo As OSVERSIONINFO
             Dim retvalue As Integer
             osinfo.dwOSVersionInfoSize = 148
             osinfo.szCSDVersion = Space$(128)
             retvalue = GetVersionExA(osinfo)
             getVersion = osinfo.dwPlatformId
          End Function
  7. Run the project and click the Command button on Form1. You should see a listing of the currently running processes.
  8. If you are running Windows 95/98, try running the example project on Windows NT or vice versa. The processes should be listed regardless of operating system version.


Portions of the code in this article were adapted from "Hardcore Visual Basic" Second Edition by Bruce McKinney - Microsoft Press

For additional information on the GetVersionExA API, please see the following article in the Microsoft Knowledge Base:
189249 : How To Determine Which 32-bit Operating System Is Being Used

For additional information on using PSAPI.DLL, please see the Microsoft Systems Journal "Under the Hood" column by Matt Pietrek (August 1996 and November 1996)


Article ID: 187913 - Last Review: July 1, 2004 - Revision: 1.2
  • Microsoft Visual Basic 5.0 Professional Edition
  • Microsoft Visual Basic 6.0 Professional Edition
  • Microsoft Visual Basic 5.0 Enterprise Edition
  • Microsoft Visual Basic 6.0 Enterprise Edition
kbhowto kbpsapi kbapi KB187913

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