RE: Function to see if a pointer is on the stack

 
I think Jon's point wasn't necessarily to use std::string, but to use a
refcounted technique with something like a smartpointer. That ensures that
your encapsulated data stays alive as long as the smartpointer does - which
can be returned, passed back by reference and so on.

Consoles are easy as you can control where the stack goes yourself and check
the range (for instance on PS2 our main thread's on the top half of the
scratchpad) but trying something like this on Windows would fill me with
dread :)

I'm curious as to what you're trying to do though, I can see the case with
strings where e.g you might want to format and return an error message (we
do this and have a string class with derivatives for stack usage and heap
usage which understand each other and know how to handle the situation of
e.g passing a string which was build up on the heap).


_____________________________
andrew grant
lead programmer, climax brighton




-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jacob
Turner (Core Design Ltd)
Sent: 20 August 2004 12:29
To: [email protected]
Subject: RE: [GD-Windows] Function to see if a pointer is on the stack

Unfortunately can't do the reliable method.  My example for copying strings
is just an example so can't use std::string<> or bare pointer technique.

Bit scared about the other option because we are in a multi-threaded app and
this function would be common to all threads and we don't have explicit
creation of common library stuff when a new thread is made.

Isn't there a really PC specific code e.g. getting the stack ptr etc.  This
is how I am doing the function on consoles.

Mind you not a big hassle because on the PC we have so much memory that
don't care if just always copy strings or whatever data i.e. can make is
variable on stack function return TRUE all the time.

Thanks

Jake

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of 
> Jon Watte
> Sent: 19 August 2004 18:19
> To: [email protected]
> Subject: RE: [GD-Windows] Function to see if a pointer is on the stack
> 
> 
> The most reliable way of doing this is to use a class for your 
> argument rather than bare pointers, and have a constructor from bare 
> pointers, and use reference counting in the class implementation -- 
> this is almost exactly what std::string<> already does for you!
> 
> Else, you can register the stack pointer in main() (or the entry 
> function for each thread/fiber), and get the stack pointer in the 
> called function, and compare -- this is not entirely portable, because 
> the stack may grow up on some architectures.
> 
> // non-threaded version -- if you use threads or fibers, // you need 
> one gBase per thread/fiber
> 
> char * gBase;
> 
> void register_main( char * base ) {
>   gBase = base;
> }
> 
> bool is_stack_pointer( char const * ptr ) {
>   char top[10];
>   assert( top < gBase ); // else stack grows up
>   return (ptr < gBase) && (ptr > top); }
> 
> int main() {
>   ...
>   char junk[ 10 ];
>   register_main( junk );
>   ...
> }
> 
> void some_func( char * anArg ) {
>   if( is_stack_pointer( anArg ) ) {
>     ...
>   }
> }
> 
> 
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of 
> Jacob Turner (Core Design Ltd)
> Sent: Thursday, August 19, 2004 9:30 AM
> To: [email protected]
> Subject: [GD-Windows] Function to see if a pointer is on the stack
> 
> 
> Is there some simple and reliable code for a console or windows app to 
> test if a pointer value is on the stack or not ?
> 
> If the pointer is on the stack (e.g. a string) then we want to copy 
> the string to heap memory for reuse later on.
> 
> Cheers
> 
> Jake
> 
> 
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