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Do I need to free BSTR variable?

Posted on 2007-11-27
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Last Modified: 2008-02-01
Hi, do I need to use SysFreeString in the following condition?
BSTR a;
_bstr_t b;
a = b.copy();
Do I need to use SysFreeString(a); when I'm done with this local variable?  I'm getting a Error in Purify tool that says I'm trying to free a freed memory in Heap memory.
Thank you.
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Question by:lapucca
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by:jkr
ID: 20360081
>>Do I need to use SysFreeString(a); when I'm done with this local variable?

No, the destructor of '_bstr_t' will care about this, that's what this utility class is good for.
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by:jkr
ID: 20360092
See also http://msdn2.microsoft.com/en-us/library/zthfhkd6(VS.80).aspx ("_bstr_t Class"):

"A _bstr_t object encapsulates the BSTR data type. The class manages resource allocation and deallocation through function calls to SysAllocString and SysFreeString and other BSTR APIs when appropriate. The _bstr_t class uses reference counting to avoid excessive overhead."
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Author Comment

by:lapucca
ID: 20360372
I just want to make sure that I understand this.  Because the BSTR variable a, is assigned the value from b.copy(), hence a doesn't need to have SysFreeString for a, because b will take care of that, right?  Because I'm not freeing _bstr_t b, I was freeing BSTR a.  Thank you.
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Author Comment

by:lapucca
ID: 20360503
I guess my question is when _bstr_t b.copy(), does this make a new BSTR that gets assign to BSTR a variable so shouldn't a be responsible for freeing the strin using SysFreeString?  Thanks.
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jkr earned 500 total points
ID: 20363459
Sorry, that somehow ended up in  my spam box - actually you should free the returned value, regardless of what that tool says.
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Expert Comment

by:mastoo
ID: 20366023
b takes care of itself.  The copy, referenced by "a" needs to be released with SysFreeString.  And I assume it was omitted for the sample posted but you don't have any string initialized in b.
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