[lug] C++ libraries in Linux

[D. Stimits]

Jeff Walker wrote:
> 
> Perhaps this is a place where C++ differs from C (I am still learning some
> of those), but if you free (delete) the string, it seems like a pointer to
> that string would be invalid.  Am I wrong?  If you copy the string, you will
> have the same problem as the original code, you have a lasting string that
> never gets free'd.

std::string creates an object that has a destructor, and it cleans up
after itself. When assigning char* type strings to std::string, it
copies by value. The leak is where the strstream is frozen, via the
.str() member function. You can then either manually delete the memory,
or you can unfreeze (non-frozen means it will clean up after itself via
destructor):
/////////////////
#include <string>
#include <strstream>

std::string paragraph( int whole, float deci )
{
	strstream buf;
	
	buf << "Paragraph: "
	    << whole
	    << ", " << deci
	    << ends;
	
	std::string rtnval = buf.str();
	buf.freeze(0);  // unfreeze.
	return rtnval;
}

int main()
{
	cout << paragraph( 2, 3.14 ) << endl;
	
	return 0;
}
/////////////////////////

> 
> Or, you could avoid the whole mess and say that this behaves like strdup(),
> where, if you use it, it allocates memory that you must free yourself.  Of
> course, I know what the "C founding fathers" would have to say about that (I
> forget who said that if you allocate memory, you should free it yourself,
> not relying of the caller to free it for you), but sometimes, you have to do
> such things. ;-)
> 
> --
> Jeff Walker                   MatchLogic, Inc.
> jwalker at matchlogic.com        7233 Church Ranch Blvd.
> Voice 1 (303) 222-2105        Westminster, CO  80021
> Fax   1 (303) 222-2001        www.matchlogic.com
> 
> -----Original Message-----
> From: Keith Brown [mailto:kbrown8 at uswest.net]
> Sent: Tuesday, September 18, 2001 10:10 AM
> To: lug at lug.boulder.co.us
> Subject: Re: [lug] C++ libraries in Linux
> 
> Hi,
> 
> I believe you have memory leak in your example.  Once you do buf.str(), the
> program owns the *char that is returned, unless it tells strstream
> otherwise,
> which I forget how to do.  I believe you need to do it like:
> 
> char * s = buf.str();
> rtnval = s;
> delete [] s;
> return rtnval;
> 
> Keith
> 
> "Scott A. Herod" wrote:
> 
> > Hi,
> >   I use something like the following:
> >
> > #include
> > <strstream>
> > string paraNode::toString()
> > {
> >     string rtnval;
> >     strstream buf;
> >
> >     buf << "Paragraph: "
> >         << ATTR_ALIGN << " = " << _align << ", "
> >         << ATTR_WRAP_MODE << " = " << _mode
> >         << ends;
> >
> >     rtnval = buf.str();
> >     return rtnval;
> > }
> >
> > > Can it be true?  There are no converters to go from an int to a string?
> Or
> > > a double to a string?
> > >
> > > --Keith
> > _______________________________________________
> > Web Page:  http://lug.boulder.co.us
> > Mailing List: http://lists.lug.boulder.co.us/mailman/listinfo/lug
> 
> --
> Keith Brown
> 12640 Xavier St
> Broomfield, CO 80020
> 303.438.8169
> 
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