Question about calling c# COM dll from c++

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4.00/5 (2 votes)

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Hi
I have a question about calling c# COM dll from c++ as below.

This is the method signature of c# COM dll

C#

public object GetData(object[] list, string view)

And this is the method signature when open tlb file from ITypeLib viewver

C++

HRESULT GetData(
                        [in] SAFEARRAY(VARIANT) list,
                        [in] BSTR view,
                        [out, retval] VARIANT* pRetVal);

And this is the c++ code that call the method

C++

SAFEARRAY* a;

    SAFEARRAYBOUND aDim[1];
    aDim[0].lLbound = 0;
    aDim[0].cElements = 1;

    a = SafeArrayCreate( VT_VARIANT, 1, aDim);

    BSTR data;
    wchar_t datawt[100];
    char tmp[100]={"TESTDATA"};
    mbstowcs(datawt,tmp,100);
    data = (BSTR)datawt;

    VARIANT vout;
    VariantInit(&vout);
    vout.vt = VT_BSTR;
    vout.bstrVal = data;

    HRESULT hr= S_OK;

    long index = 0;
    if(hr = SafeArrayPutElement(a,&index,&vout))
    {
        SafeArrayDestroy(a);
    }
    _variant_t result = k->GetData(a,"VIEW");

I've found there is an object array which has lenght is 1 as the c++ code when COM dll is called but the data in the object array is blank.

Does anyone know why the data is blank and what is the solution for this problem ?

Thx

Posted 18-Apr-10 22:24pm

lonely_emotion

Updated 19-Apr-10 0:09am

v2

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Comments

PotatisPulver 3-Aug-10 12:05pm

Reason for my vote of 4
clear code

2 solutions

Solution 2

Call like this: k->GetData(a,"VIEW"); doesn't look good.

When passing a text string into COM, always pass a new instance of BSTR, which then will be deallocated by COM run-time.

In the example above, you should pass _bstr_t(_T("VIEW")).copy();

Posted 3-May-10 7:54am

Vitaly Tomilov

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kartikdasani · Accepted Answer · 2010-04-19T20:01:00

Solution 1

try using :

C#

vout.bstrVal = _bstr_t("TESTDATA");

instead of :

C#

wchar_t datawt[100];
char tmp[100]={"TESTDATA"};
mbstowcs(datawt,tmp,100);
data = (BSTR)datawt;

Posted 19-Apr-10 20:01pm

kartikdasani