problems with Pass by Reference

[bg_ie]

I have a function as follows -

long Read (char* databuf)
{
/* start missing */

databuf = new char [datasize];
file.read (databuf, datasize);
return datasize;
}

I call it as follows -

char* databuf = NULL;
long datasize = Read (databuf);

The problem is that databuf is still NULL after that call to Read(). I
understand why, but how should I do this?

Thanks,

Barry.

[Frederick Gotham]

The problem is that databuf is still NULL after that call to Read(). I
understand why, but how should I do this?

You want a reference to a pointer:

long Read(char *&p)
{
p = new char[10];
return 10;
}

int main()
{
char *p;

Read(p);

delete [] p;
}

--

Frederick Gotham

[Morten V Pedersen]

Frederick Gotham wrote:

>The problem is that databuf is still NULL after that call to Read(). I
understand why, but how should I do this?

You want a reference to a pointer:

long Read(char *&p)
{
p = new char[10];
return 10;
}

int main()
{
char *p;

Read(p);

delete [] p;
}

Yes you need a *reference to pointer* or *pointer to pointer* the reason
is that you actually passing the pointer by value - what does that mean?

When you call Read(..) a temp copy of you databuf pointer is created
pointing to NULL, this is then passed to Read(..) - so every change you
make to the databuf inside Read(..) is only performed on the temp copy
and when Read(..) returns the original databuf will remain unchanged.

Did that make sense to you?

--
// morten