Specified cast is not valid issue?

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trying to call Find() from a test dll im messing with and I keep getting the error"Specified cast is not valid."

here's a little snippet of what im working with.....

test.dll
foo.h

C++

__declspec(dllexport) UINT Find();

foo.cpp

C++

UINT Find()
{
	return 1;
}

C# test.exe using interface for the call

C#

[ComImport, CoClass(typeof(object)), TypeIdentifier, CompilerGenerated, Guid("MYGUID")]
    public interface CSmart : ISmart
    {
    }

    [ComImport, TypeIdentifier, CompilerGenerated, Guid("MYGUID")]
    public interface ISmart
    {
        [DispId(1)]
        uint Find();
}

here is the button push

C#

private CSmart caller;
this.caller = (CSmart)Activator.CreateInstance(Type.GetTypeFromCLSID(new Guid("MYGUID")));
           try
           {
               caller.Find(); //<---here is when the error pops
           }catch (Exception ex)
           {
               //Specified cast is not valid.
           }

Loading the dll into dependancy walker shows

C

1(0x0001) | 0(0x0000) | unsigned int Find(void) | 0x00011091

What I have tried:

not sure where to start....lol

Posted 10-Feb-16 9:02am

JEEPRFAM

Updated 10-Feb-16 9:14am

v3

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Comments

Philippe Mori 12-Feb-16 20:16pm

I don't understand your question. C/C++ code seems to be regular functions exported from the DLL while C# code seems to use COM object. You have to select one technology and used the same on both side. As such, that question does not make much sense.

1 solution

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Aescleal · Answer 1 · 2016-02-10T10:49:00

Solution 1

Your exported function doesn't look like a COM object to me. I'm not a great expert on C# but if all you've got is a C function can't you just call it directly after importing it:

C#

class urgle
{
    [DllImport("test.dll")] public static extern UINT Find();
};

is the sort of thing you need.

Posted 10-Feb-16 10:49am

Aescleal

Comments

JEEPRFAM 10-Feb-16 17:48pm

the test.dll has a bunch of other functions ex. DllCanUnloadNow, DllGetClassObject, DllInstall, DllRegisterServer, DllUnregisterServer ect.... to work with COM, I'm able to register it and it loads using Activator.CreateInstance im just having a hard time figuring out how to code the dll (not the best at c++) to work with the interface layout i have
<pre lang="c#">
[ComImport, TypeIdentifier, CompilerGenerated, Guid("MYGUID")]
public interface ISmart
{
[DispId(1)]
uint Find();
}
</pre>

so in other words to figure out what code is needed in the dll to work with that interface layout. if that makes any sense lol
Thanks for your response though

JEEPRFAM 11-Feb-16 11:48am

we'll I think im getting closer now when calling Find() im getting this error -> Attempted to read or write protected memory. This is often an indication that other memory is corrupt.