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Converting variables...

Posted on 1999-01-11
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Last Modified: 2008-02-01
How do I copy a BSTR variable to a char variable?

How do I copy a char variable (of array type) to a BSTR variable?
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Question by:loyaliser
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6 Comments
 
LVL 10

Expert Comment

by:viktornet
ID: 1181868
What's a BSTR?
0
 
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Author Comment

by:loyaliser
ID: 1181869
BSTR is a COM variable type. I am building a COM in Visual C++ 6.0 and one of my functions accepts a parameter of type BSTR. I need to convert the BSTR variable to a char so that I can pass it to a function that accepts a char parameter.

That's it... make any sense? Thanks...
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Author Comment

by:loyaliser
ID: 1181870
As far as I know BSTR is similar to the String data type, however, I don't know if it shares the same API methods.
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LVL 1

Expert Comment

by:fkurucz
ID: 1181871
the class _bstr_t defined in <comdef.h> automates the conversion from and to BSTR or char*.

intern the following functions are used:

 BSTR _com_util::ConvertStringToBSTR(const char* pSrc)

 char* _com_util::ConvertBSTRToString(BSTR pSrc)

bye,
  feri
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Accepted Solution

by:
rayb earned 80 total points
ID: 1181872

There are several ways to perform this action.  One I frequently use is snprintf, which can do the job like this:
{
  const int
    max= 255;
  char
    buffer[max];

  _snprintf( buffer, max, "%S", your_bstr_here );
}

Notice that the "%S" is a capital S.

Although this method works, the preferred method is to use the WideCharToMultiByte function.

Another preferred method works in the context of ATL and uses the USES_CONVERSION and W2A macros.

To do the inverse of these operations, use the MultiByteToWideChar, SysAllocString, USES_CONVERSION and A2W functions and macros.

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LVL 1

Author Comment

by:loyaliser
ID: 1181873
Yeah... I need the method that works in the ATL, because the code is within an ATL COM object.

Thanks...
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