CeGetSystemInfo doesn't fill the struct passed by reference

Question

I'm trying to get information about a Windows Mobile device from a desktop application (written in C#). I searched the MSDN and found that the function I need is in rapi.dll:

VOID CeGetSystemInfo (LPSYSTEM_INFO lpSystemInfo);

The parameter is a pointer to a struct which is deffined like this:

typedef struct _SYSTEM_INFO {
    union {
       DWORD dwOemId;
       struct {
          WORD wProcessorArchitecture;
          WORD wReserved;
       };
    };
    DWORD dwPageSize;
    LPVOID lpMinimumApplicationAddress;
    LPVOID lpMaximumApplicationAddress;
    DWORD dwActiveProcessorMask;
    DWORD dwNumberOfProcessors;
    DWORD dwProcessorType;
    DWORD dwAllocationGranularity;
    WORD wProcessorLevel;
    WORD wProcessorRevision;
} SYSTEM_INFO, *LPSYSTEM_INFO;

Here is how I mapped it all to managed code:

[DllImport("rapi.dll")]
public static extern void CeGetSystemInfo([MarshalAs(UnmanagedType.Struct)]ref SYSTEM_INFO info);

[StructLayout(LayoutKind.Sequential)]
public struct SYSTEM_INFO
{
       internal PROCESSOR_INFO_UNION uProcessorInfo;
       public uint dwPageSize;
       public IntPtr lpMinimumApplicationAddress;
       public IntPtr lpMaximumApplicationAddress;
       public uint dwActiveProcessorMask;
       public uint dwNumberOfProcessors;
       public uint dwProcessorType;
       public uint dwAllocationGranularity;
       public ushort wProcessorLevel;
       public ushort wProcessorRevision;
}

[StructLayout(LayoutKind.Explicit)]
public struct PROCESSOR_INFO_UNION
{
       [FieldOffset(0)]
       internal uint dwOemId;
       [FieldOffset(1)]
       internal ushort wProcessorArchitecture;
       [FieldOffset(2)]
       internal ushort wReserved;
}

When I call the function passing the SYSTEM_INFO struct nothing happens. The function does not alter the values of the struct in any way. Have I mapped the struct wrong or something?

Thanks in advance

Does this actually work? Your managed definition of PROCESSOR_INFO_UNION doesn't match what's in SYSTEM_INFO, offsetting all of your other members by 4 bytes. — ctacke, Feb 10 '10 at 16:07

score 0 · Accepted Answer · answered Feb 10 '10 at 15:37

0

Got it!

The rapi.dll needs to be initialized by calling the CeRapiInit function and then after all your function calls you need to close the rapi by calling CeRapiUinit

answered Feb 10 '10 at 15:37

Raphael

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CeGetSystemInfo doesn't fill the struct passed by reference

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