VB / C++ COM BSTR question

[John2069]

Not sure if this is more a VB or C++ question, posted on both.

I have a C++ dll with a function that is used
in VB code.

The C++ function returns a BSTR to the VB calling functions. This function is called ALOT by various VB function.

The problem:

After much processing (1 hour+), memory is consumed like crazy, 200M and up. We (the team that must debug this) think the BSTR's aren't being free'd in VB. We know this should be done automagically. I will test this theory today.

If that is the case how can we free the BSTR memory in the VB code. I only know of:
bstrVar = Nothing
or
bstrVar = ""

Could I create a method in the C++ class that returns the memory with SysFreeString? May get a pointer from the VB code as a func parameter?

any ideas are welcome.

[nabeels786]

to free string mem in VB, just assign it a zero-length value

Dim myStr As String
 
myStr = "hello"
 
'free it
myStr = ""

i think in c++, you do

char *mystring = new char[<maxlength>];

//free if
free (mystring) 

i haven't use BSTR, so I wouldn't know..sorry

[Zaei]

Take the return string as a parameter to the DLL function. That way, it is up to VB to create and delete the string.

Z.

[parksie]

char *mystring = new char[<maxlength>];

//free if
free (mystring)

Ick ick ick

char *mystring = new char[<maxlength>];

//free if
delete[] mystring;

Don't use free and new on the same pointer.

[THEROB]

Try setting the object to nothing

So:

set obj = createobject("the.c++object")

ret = obj.thefunctioncall

set obj = nothing

this should free the c++ object.


Bye the way, the BSTR is only 65537 (In borland anyway) characters long so if you need any more you need to write this to a file.

[nabeels786]

Originally posted by parksie

char *mystring = new char[<maxlength>];

//free if
free (mystring)

Ick ick ick

char *mystring = new char[<maxlength>];

//free if
delete[] mystring;

Don't use free and new on the same pointer.

ah okay...maybe thats why...

i learned something today