c# - P/Invoking CreateToolhelp32Snapshot failing in Compact Framework

Question

Hey, im doing a little app for my smart phone, using Windows Mobile 6. I'm trying to get all currently running processec, but method CreateToolhelp32Snapshot always returns -1. So now im stuck. I tried to get error with invoking GetLastError() method, but that method returns 0 value. Here is a snippet of my code.

private const int TH32CS_SNAPPROCESS = 0x00000002;
[DllImport("toolhelp.dll")]
public static extern IntPtr CreateToolhelp32Snapshot(uint flags, 
                                                     uint processid);

public static Process[] GetProcesses()
    {
        ArrayList procList = new ArrayList();
        IntPtr handle = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);

        if ((int)handle > 0)
        {
            try
            {
                PROCESSENTRY32 peCurr;
                PROCESSENTRY32 pe32 = new PROCESSENTRY32();

                // get byte array to pass to API call
                byte[] peBytes = pe32.ToByteArray();
                // get the first process
                int retval = Process32First(handle, peBytes);

Answer 1

• First, your handle check is wrong. It's common for the high bit to be on in a handle, causing it to look like a negative number when cast to a signed int. You should be checking that is isn't NULL (0) or INVALID_HANDLE_VALUE (-1 / 0xffffffff).
• You shouldn't be "invoking GetLastError" but calling Marshal.GetLastWin32Error()
• You've not set the SetLastError attribute in the P/Invoke declaration. In C# it defaults to false, in VB it defaults to true.
• Where's your PROCESS32 implementation? The docs clearly state that the dwLength member must be set before the call and it's not clear here if that's happening.

As a side note, the Smart Device Framework's OpenNETCF.ToolHelp namespace has all of this implemented and working (in case you'd rather not reinvent the wheel).