Passing a managed (C#) string[] array to a COM DLL

Question

Setup:
I have a COM DLL that calls a method inside a managed C# DLL. This function returns a C# string[] array, which is marshaled to a SAFEARRAY.

Problem:
When I try to access the strings within the safearray I only get the first char of the string. What am I doing wrong?

The code:

    // Pointer to the managed interface
    DatabasePtr pODB(__uuidof(DBClass));

    // Get the string[] array from the managed method
    SAFEARRAY* safearray = pODB->GetStringArray();

    HRESULT hresult;

    long ubound;
    long lbound;

    hresult = SafeArrayGetUBound(safearray, 1, &ubound);
    hresult = SafeArrayGetLBound(safearray, 1, &lbound);

    long index;
    BSTR fromarray;

    for (; lbound <= ubound; lbound++)
    {
        index = lbound;

        hresult = SafeArrayGetElement(safearray, &index, (void*)&fromarray);

        char buffer[512];
        sprintf_s(buffer,"%s",fromarray);

        MessageBox(0, (LPCSTR)buffer, "...", 0);
    }

Thanks for your help,
-Sean!

Remus Rusanu · Accepted Answer · 2009-05-17 23:27:28Z

2

The BSTR is an unicode string, so you must use an wchar_t buffer and the wsprintf_s. Right now u print the ANSI part of the first unicode character then stop on the \0. And please, please, don't stack overflow like that (sic!). Use the safe _vsnwprintf_s_l and its family, your code is a hacker's delight as it is right now and u'll be pwned. See http://msdn.microsoft.com/en-us/library/d3xd30zz(VS.80).aspx

answered May 17, 2009 at 23:27

Remus Rusanu

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7 Comments

Sean Over a year ago

Thanks for the help. What do you mean by, "don't stack overflow like that?"

Remus Rusanu Over a year ago

sprintf will overflow buffer if fromarray is bigger that 512

Sean Over a year ago

Alright. It won't be bigger than 512, but I'll go w/ the safe route anyways. Thanks again.

Sean Over a year ago

Also, you didn't mention that I should've been using MessageBoxW, instead of MessageBox...

Remus Rusanu Over a year ago

right, and your database routines access also. You may want to use the generic TCHAR type and change the project settings to Unicode. Or, if you must stick to ANSI, convert the received fromarray to ANSI first via something like MultiByteToWideChar (msdn.microsoft.com/en-us/library/dd319072(VS.85).aspx). Also you should look into the BSTR wrapper helpers, _bstr_t and CComBSTR. I prefer _bstr_t see msdn.microsoft.com/en-us/library/zthfhkd6(VS.80).aspx

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