Do I need to free BSTR variable?

Posted on 2007-11-27
Medium Priority
Last Modified: 2008-02-01
Hi, do I need to use SysFreeString in the following condition?
_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.
Question by:lapucca
  • 3
  • 2
LVL 86

Expert Comment

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.
LVL 86

Expert Comment

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."

Author Comment

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.
7 new features that'll make your work life better

It’s our mission to create a product that solves the huge challenges you face at work every day. In case you missed it, here are 7 delightful things we've added recently to monday to make it even more awesome.


Author Comment

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.
LVL 86

Accepted Solution

jkr earned 2000 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.
LVL 21

Expert Comment

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.

Featured Post

Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Errors will happen. It is a fact of life for the programmer. How and when errors are detected have a great impact on quality and cost of a product. It is better to detect errors at compile time, when possible and practical. Errors that make their wa…
Written by John Humphreys C++ Threading and the POSIX Library This article will cover the basic information that you need to know in order to make use of the POSIX threading library available for C and C++ on UNIX and most Linux systems.   [s…
The viewer will learn how to user default arguments when defining functions. This method of defining functions will be contrasted with the non-default-argument of defining functions.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

600 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question