Re: Passing pointer between DLL boundary question

From:

"KMA" <kma@schneeberger.ch>

Newsgroups:

comp.os.ms-windows.programmer.win32,microsoft.public.vc.mfc

Date:

Tue, 18 Jul 2006 16:44:21 +0200

Message-ID:

<e9is3l$3p9$1@atlas.ip-plus.net>

"AliR" <AliR@online.nospam> wrote in message
news:44bcf246$0$23758$a8266bb1@reader.corenews.com...

Why would creating global memory in a dll and freeing it in the
application
be a problem?

In itself it isn't. But it's hard to ensure that the application writer
plays by the rules. Unless the app writer is given clear instructions about
who should delete what then even the good-willed app writers can't know what
to do.

AliR.

<indrawati.yahya@gmail.com> wrote in message
news:1153224364.650528.89470@i42g2000cwa.googlegroups.com...

Hi

This may be a stupid question, but I want to make sure my understanding
is correct. I understand that allocating a memory inside a DLL and
freeing the memory in the program that uses the DLL (or vice versa) is
not a good idea, but if a pointer passed between a DLL boundary is
allocated and freed at the correct place, is the code guaranteed to be
safe? For example:

1. In dll implementation code:

static const char someString[] = "a string";

void GetString(const char** ps)
{
     if(ps)
         *ps = &(someString[0]);
}

And in application code:

const char* aString;
GetString(&aString);
cout << aString;

2. Another example: in dll implementation code:

static void* data = 0;
static int dataSize = 0;

///... functions that manipulate data

int GetData(void* buff, int buffSize)
{
    if(buff && buffSize >= dataSize)
    {
        memcpy(buff, data, dataSize);
        return dataSize;
    }
    return 0;
}
(buff is a buffer allocated and freed in the application).

I tried on my VC++ 6, both examples run fine, but are they always
guaranteed to be safe? Are there any side effects that I should be
aware of? Thanks!