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BSTR Problem!

Posted on 2001-06-13
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Last Modified: 2013-11-20
Hi,

I am using an automation component which was developed by someone else?


After importing the corresponding *.tlb file,
the complier will genearte one *.tlh file which contain the following code!

__declspec(implementation_key(191))
HRESULT IFnVersionableDual::Checkout ( BSTR * CheckoutPath, _bstr_t Directory, _bstr_t FileName, const _variant_t & Options );

When I use the Checkout method,
I want to know how can I enter the paramter correctly.

I have tried this:

MyObject->Checkout("c:\\test.txt", "c:\\", "test.txt");

But it cannot be complied

The erros is cannot convert parameter 1 from 'char [1]' to 'unsigned short ** '.

How can I correct this problem?

Thanks!
0
Comment
Question by:cplau
  • 7
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  • +3
18 Comments
 
LVL 2

Expert Comment

by:missionImpossible
ID: 6185040
use the _T()-macro:

MyObject->Checkout(
  _T("c:\\test.txt"),
  _T("c:\\"),
  _T( "test.txt")  );


0
 
LVL 42

Expert Comment

by:sedgwick
ID: 6185045
use AllocSysString():

     CString str("Hockey is Best!");
     BSTR bstr = str.AllocSysString();

good luck
0
 
LVL 2

Expert Comment

by:missionImpossible
ID: 6185064
sorry, for the first parameter you should do the following:

_bstr_t CheckOutPath ( _T("c:\\test.txt") );

MyObject->Checkout(
 CheckOutPath,
 _T("c:\\"),
 _T( "test.txt")  );
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Expert Comment

by:SrinivasaRao
ID: 6185069
BSTR was defined as unsigned short* . So please use unsigned short** in the place of BSTR*. I hope this will solve your problem.
BSR
0
 
LVL 6

Expert Comment

by:snoegler
ID: 6185197
>>     CString str("Hockey is Best!");
>>    BSTR bstr = str.AllocSysString();

If you use this code, you have to add an ::SysFreeString(bstr); later!

Instead of allocating a BSTR this way, you can also

1. #include <afxpriv.h>
2. Place an USES_CONVERSION; as the first line of the function.
3. Use T2OLE() to convert from the TCHAR to BSTR/OLECHAR.

->
#include <afxpriv.h>

void doit()
{
USES_CONVERSION;
MyObject->Checkout(T2OLE(_T("c:\\test.txt")), T2OLE(_T("c:\\")), T2OLE(_T("test.txt")));
}
0
 

Author Comment

by:cplau
ID: 6185279
Hi All,

In the tlh file, I also found this code,
 __declspec(property(get=GetNumber))
    _bstr_t Number;

When I try to read this object's properties like this

MyObject->Number

Do I need to do any coversion to get the correct value?

Thanks!
0
 
LVL 42

Expert Comment

by:sedgwick
ID: 6185295
i still think that it better that u maintain your allocation and free instead of rely on the systme

0
 
LVL 2

Expert Comment

by:missionImpossible
ID: 6185296
_bstr_t is a wrapper-class for BSTR, so you can read the Number-property like you suggest. There is no conversion needed.
0
 
LVL 9

Expert Comment

by:ShaunWilde
ID: 6185375
first of all is CheckoutPath an [in],[out],[in,out] parameter - what is in the idl?

this will determine how we deal with it - because it is a BSTR* then I suspect it is an [out] or [in,out] - however it could have just been defined incorrectly

if [out]

_bstr_t bstrCheckout;
MyObject->Checkout(&bstrCheckout, "c:\\", "test.txt");

if [in,out]
_bstr_t bstrCheckout(_T("c:\\test.txt"));
MyObject->Checkout(&bstrCheckout, _T("c:\\"), _T("test.txt"));

I hope this helps



0
 
LVL 9

Expert Comment

by:ShaunWilde
ID: 6185390
however you may have to do it like this if _bstr_t doesn't support & operator to return a pointer to its internal BSTR (which I know CComBSTR does)

if [out]

BSTR bstrCheckout=NULL;
MyObject->Checkout(&bstrCheckout, "c:\\", "test.txt");

::SysFreeString(bstrCheckout);


if [in,out]
BSTR bstrCheckout=::SysAllocString(T2W((_T("c:\\test.txt"))));
MyObject->Checkout(&bstrCheckout, _T("c:\\"), _T("test.txt"));

::SysFreeString(bstrCheckout);
0
 

Author Comment

by:cplau
ID: 6185438
Dear All,

At my first question,

__declspec(implementation_key(191))
HRESULT IFnVersionableDual::Checkout ( BSTR * CheckoutPath, _bstr_t Directory, _bstr_t FileName, const
_variant_t & Options );

The fourth paramter is the optional paramter

CString str("c:\\yyee.txt");
BSTR bstr = str.AllocSysString();
CString str1("c:\\");
BSTR bstr1 = str1.AllocSysString();
CString str2("yyee.txt");
BSTR bstr2 = str2.AllocSysString();

COleVariant name(1);

Temp->Checkout(&bstr,bstr1,bstr2,name);

But the following error :
COleVariant::COleVariant' : ambiguous call to overloaded function

I've also tried using this
ColeVairant name("%d", 1);

But the program crash while running!

What mistake had I made?
How can I input the fourth parameter with a value of 1?

Thanks!
0
 
LVL 42

Expert Comment

by:sedgwick
ID: 6185633
cplau: initialaize the 'name' like this:

COleVariant name(1.0);

and it will work... :)
0
 
LVL 42

Expert Comment

by:sedgwick
ID: 6185634
cplau: initialaize the 'name' like this:

COleVariant name(1.0);

and it will work... :)
0
 
LVL 42

Expert Comment

by:sedgwick
ID: 6185648
or even better:

     COleVariant name((short)1); !!!

since there's no constructor for int...

cheer
0
 
LVL 9

Accepted Solution

by:
ShaunWilde earned 150 total points
ID: 6186161
remember to free your BSTRs that you allocated or else it will leak

CString str("c:\\yyee.txt");
BSTR bstr = str.AllocSysString();

// your code


::SysFreeString(bstr);


> COleVariant::COleVariant' : ambiguous call to overloaded function

use COleVariant name((short)1); // for VT_I2
or COleVariant name((long)1); // for VT_I4
or COleVariant name(1,VT_I2);
or COleVariant name(1,VT_I4);

> ColeVairant name("%d", 1);
COleVariant does not do string formatting - you were telling the variant that the string being passed in was actually a VT_NULL




0
 
LVL 42

Expert Comment

by:sedgwick
ID: 6190149
great, using my comment to get the points
0
 
LVL 6

Expert Comment

by:snoegler
ID: 6190180
Isn't this the point there was a quite lengthy discussion about a short time ago?
:-/
0
 
LVL 42

Expert Comment

by:sedgwick
ID: 6190581
whatever
0

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