C# dll, C++ client, pass array parameter

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Hello,
I have a C# DLL with a call like this:

[DispId(7)]
void Test([MarshalAs(UnmanagedType.SafeArray,
                      SafeArraySubType = VarEnum.VT_BSTR)] ref string[] s);

On the C++ side, the function is called:

SAFEARRAY *sArr1 = NULL;
iface.Test(&sArr1);

I'm getting a message box: "The parameter is incorrect."

Looking at the output debugging window, I see this:
Warning: constructing COleException, scode = E_INVALIDARG ($80070057).

Does anyone know of other ways to pass an array as a parameter, C# DLL and C++ client?

Any help would be appreciated.

Sincerely,
Mike

Posted 6-Dec-10 11:08am

mla154

Updated 7-Dec-10 3:41am

v3

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2 solutions

Solution 1

Admittedly, I can't read C#, but hopefully you'll get some help from this post anyway.

Something I noticed; you have a variable sArr1, which is a pointer to a SAFEARRAY. When you call your Test function, the argument is a pointer to this pointer to a SAFEARRAY; you should maybe call it like so:

SAFEARRAY *sArr1 = NULL;
iface.Test(sArr1);

It's not impossible you actually want to use this double pointer though.

Second idea; the message box comes from within the DLL, it may simply be complaining about the NULL-value.

Posted 6-Dec-10 11:23am

User 7429338

Updated 6-Dec-10 11:30am

v3

Comments

mla154 6-Dec-10 17:29pm

The argument is of type SAFEARRAY**.

mla154 7-Dec-10 9:29am

It may be complaining about the NULL-value, but I have tried other things as well, such as:

//C++ code
SAFEARRAYBOUND sab[1];
SAFEARRAY *sArr1;

sab[0].cElements = 0;
sab[0].lLbound = 0;
sArr1 = SafeArrayCreate(VT_BSTR, 1, (SAFEARRAYBOUND*)&sab);
iface.Test(&sArr1);

mla154 7-Dec-10 9:38am

It's hard to say whether the message box comes from within the DLL. I placed this message box code as the first line of the C# function, and the message box was never displayed:

MessageBox.Show("here");

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mla154 · Accepted Answer · 2010-12-07T04:21:00

Solution 2

OK, I found a solution to my problem.

//C# DLL
public void Test(ref object s)
{
   s = new string[2] { "one", "three" };
}

//C++ call
VARIANT s = COleVariant();
BOOL b = iface.CreateDispatch( ... );  //Parameter omitted for conciseness
iface.Test(&s);

Thank you all for your efforts.

Posted 7-Dec-10 4:21am

mla154