C ++库问题

Question

I'm trying to make a call to a C++ library from my C# code. I also have a sample application written in C++ that invokes the same library, and works fine. However, the call from C# throws an error:

Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

The c# code is:

#region DllImports

[DllImport("kernel32.dll", EntryPoint = "LoadLibrary")]
static extern int LoadLibrary([MarshalAs(UnmanagedType.LPStr)] string lpLibFileName);

[DllImport("kernel32.dll", EntryPoint = "GetProcAddress")]
static extern IntPtr GetProcAddress(int hModule, [MarshalAs(UnmanagedType.LPStr)] string lpProcName);

[DllImport("kernel32.dll", EntryPoint = "FreeLibrary")]
static extern bool FreeLibrary(int hModule);

[UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]
delegate string bondProbeCalc(string licenseFolder, string requestString);

#endregion


/// <summary>
/// Calls Bondprobe to calculate a formula
/// </summary>
internal static string DoBondProbeOperation(string requestString)
{
    if (string.IsNullOrEmpty(requestString)) throw new ArgumentNullException();

    //Reference library
    int hModule = LoadLibrary(ConfigurationManager.Instance.BondProbeSettings.AssemblyFilePath);

    if (hModule != 0)
    {
        IntPtr intPtr = GetProcAddress(hModule, "bpStringCalc");

        bondProbeCalc funcDelegate = (bondProbeCalc)Marshal.GetDelegateForFunctionPointer(intPtr, typeof(bondProbeCalc));

        requestString = requestString.EndsWith("=") ? requestString.Substring(0, requestString.Length - 1) : requestString;

        string returnValue = funcDelegate(ConfigurationManager.Instance.BondProbeSettings.LicenseFilePath, requestString);

        FreeLibrary(hModule);

        return returnValue;
    }

    return string.Empty;
}

This exact same code works on some computers, and it throws the error on others. However, the sample C++ app seems to work everywhere.

Any ideas?

Thanks, Gonzalo

Answer 1

I'm guessing the crashing is occurring on computers running 64-bit OSs. I don't know about your DoBondProbeOperation logic, but your PInvoke methods should be defined as follows:

[DllImport("kernel32.dll", CharSet = CharSet.Auto]
static extern IntPtr LoadLibrary(string lpFileName);

[DllImport("kernel32.dll"]
static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName);

[DllImport("kernel32.dll"]
static extern bool FreeLibrary(IntPtr hModule);

Where you compare hModule to 0 , instead compare to IntPtr.Zero

EDIT: Fixed CharSet value for LoadLibrary

EDIT2: Also try changing your bondProbeCalc definition to the following:

[UnmanagedFunctionPointer(CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
delegate string bondProbeCalc(string licenseFolder, string requestString);

Or:

[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
delegate [MarshalAs(UnmanagedType.LPStr)] string bondProbeCalc([MarshalAs(UnmanagedType.LPStr)] string licenseFolder, [MarshalAs(UnmanagedType.LPStr)] string requestString);

Answer 2

Comments on Marshal.GetDelegateForFunctionPointer indicate that calling conventions other than Stdcall are not supported, ie that specifying [UnmanagedFunctionPointer(CallingConvention.Cdecl)] on your delegate type is not effective. If this is indeed the case, you'll need to switch to using PInvoke to call bpStringCalc , recompile the native library to export the function with the __stdcall modifier, or write a shim in C++/CLI (as IJW interop would not have this calling convention restriction).