Question

I have to call a C++ DLL from my C# program.
I’m trying to do it using PInvoke – everything works fine in VS2005\ 2008, but after migration to VS 2010, I get this exception:

PInvokeStackImbalance was detected
Message: A call to PInvoke function
‘sampleFunc’ has unbalanced the stack.
This is likely because the managed
PInvoke signature does not match the
unmanaged target signature. Check that
the calling convention and parameters
of the PInvoke signature match the
target unmanaged signature.

This is the original C++ prototype:

typedef struct {
    unsigned short field1;
    unsigned short field2;
} sInfo;

_declspec(dllexport) int sampleFunc(sInfo *info, char *txt);

and here is the C# code:

[StructLayout(LayoutKind.Sequential)]
    struct SInfo
    {
        //[MarshalAs(UnmanagedType.U1)] //also tried with the MarshalAs attr. Didn't help.
        public ushort field1;
        //[MarshalAs(UnmanagedType.U1)]
        public ushort field2;
    };
[DllImport("sampleModule.dll", CharSet=CharSet.Ansi)]
        public static extern int sampleFunc(ref SInfo info, [MarshalAs(UnmanagedType.LPStr)] string txt);

I’ve tried it also with IntPtr instead of the ref SInfo, but got the same result…

Any help will be appreciated,

Thank you all!

Answer 1

Hard to see how this could have worked before. The C++ declaration doesn’t declare the calling convention, the default is __cdecl unless overridden in the C++ project with the /Gz compile option. You have to tell the P/Invoke marshaller:

    [DllImport("sampleModule.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
    public static extern int sampleFunc(ref SInfo info, string txt);