what exactly is the danger of an uninitialized pointer in C
- by akh2103
I am trying get a handle on C as I work my way thru Jim Trevor's "Cyclone: A safe dialect of C" for a PL class. Trevor and his co-authors are trying to make a safe version of C, so they eliminate uninitialized pointers in their language. Googling around a bit on uninitialized pointers, it seems like un-initialized pointers point to random locations in memory. It seems like this alone makes them unsafe. If you reference an un-itilialized pointer, you jump to an unsafe part of memory. Period. But the way Trevor talks about them seems to imply that it is more complex. He cites the following code, and explains that when the function FrmGetObjectIndex dereferences f, it isn’t accessing a valid pointer, but rather an unpredictable address — whatever was on the stack when the space for f was allocated.
What does Trevor mean by "whatever was on the stack when the space for f was allocated"? Are "un-initialized" pointers initialized to random locations in memory by default? Or does their "random" behavior have to do with the memory allocated for these pointers getting filled with strange values (that are then referenced) because of unexpected behavior on the stack.
Form *f;
switch (event->eType) {
case frmOpenEvent:
f = FrmGetActiveForm(); ...
case ctlSelectEvent:
i = FrmGetObjectIndex(f, field); ...
}
