Hi All,
I am facing a strange problem..
I am calling a function func2 from func1. Before calling func2 all
the local variables in func1 looks fine and has their respective
values. When function returns back from func2 to func1 all the local
variables in func1 has values 0xfdfdfd.
Can somebody please explain me what is happening and what is the
solution for this?
Thanks
Trupti
8  1941  Sa***********@g mail.com wrote:
I am facing a strange problem..
I am calling a function func2 from func1. Before calling func2 all
the local variables in func1 looks fine and has their respective
values. When function returns back from func2 to func1 all the local
variables in func1 has values 0xfdfdfd.
Can somebody please explain me what is happening and what is the
solution for this?
That sounds very much like stack corruption or deletion of something
that was allocated outside of the free store (both are instances of
undefined behaviour). Without seeing what 'func2' does it is impossible
to give you a specific recommendation, but see if it tries to call
delete on a pointer to some 'func1's local data.
V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask
Hi All,
>
* I am facing a strange problem..
I am calling a function func2 from func1. *Before calling func2 all
the local variables in func1 looks fine and has their respective
values. *When function returns back from func2 to func1 all the local
variables in func1 has values 0xfdfdfd.
*Can somebody please explain me what is happening and what is the
solution for this?
Post some code so we can take a look at it.
On Mon, 16 Jun 2008 06:41:18 -0700, Sa***********@g mail.com wrote:
Hi All,
I am facing a strange problem..
I am calling a function func2 from func1. Before calling func2 all the
local variables in func1 looks fine and has their respective values.
When function returns back from func2 to func1 all the local variables
in func1 has values 0xfdfdfd.
Can somebody please explain me what is happening and what is the
solution for this?
Post code. http://www.parashift.com/c++-faq-lit...t.html#faq-5.8
--
Lionel B
"Sa***********@ gmail.com" <Sa***********@ gmail.comwrites :
Hi All,
I am facing a strange problem..
I am calling a function func2 from func1. Before calling func2 all
the local variables in func1 looks fine and has their respective
values. When function returns back from func2 to func1 all the local
variables in func1 has values 0xfdfdfd.
Can somebody please explain me what is happening and what is the
solution for this?
There's probably a "buffer overflow" or some other kind of overrun in
the local variables of func2. In the usual processors, the stack
grows downward, and the local variables are allocated on the stack.
So the local variables of func2 are stored before the the local
variables of func1, and if you write beyond the bounds of the local
variables of func2, you can erase the frame pointers, the return
addresses and the local variables of the calling procedures.
The solution would be to debug func2.
--
__Pascal Bourguignon__
On Jun 16, 7:34*pm, p...@informatim ago.com (Pascal J. Bourguignon)
wrote:
"Samant.Tru...@ gmail.com" <Samant.Tru...@ gmail.comwrites :
Hi All,
* I am facing a strange problem..
I am calling a function func2 from func1. *Before calling func2 all
the local variables in func1 looks fine and has their respective
values. *When function returns back from func2 to func1 all the local
variables in func1 has values 0xfdfdfd.
*Can somebody please explain me what is happening and what is the
solution for this?
There's probably a "buffer overflow" or some other kind of overrun in
the local variables of func2. *In the usual processors, the stack
grows downward, and the local variables are allocated on the stack.
So the local variables of func2 are stored before the the local
variables of func1, and if you write beyond the bounds of the local
variables of func2, you can erase the frame pointers, the return
addresses and the local variables of the calling procedures.
The solution would be to debug func2.
--
__Pascal Bourguignon__
Thank you for quick reply for my query. It is not possible for me to
post code. It is a big application and lots of variables.
I will try to debug it according your suggestions. Please post me
some more suggestions if any.
Trupti Sa***********@g mail.com wrote:
On Jun 16, 7:34 pm, p...@informatim ago.com (Pascal J. Bourguignon)
wrote:
>"Samant.Tru... @gmail.com" <Samant.Tru...@ gmail.comwrites :
>>Hi All,
I am facing a strange problem..
I am calling a function func2 from func1. Before calling func2 all
the local variables in func1 looks fine and has their respective
values. When function returns back from func2 to func1 all the local
variables in func1 has values 0xfdfdfd.
Can somebody please explain me what is happening and what is the
solution for this?
There's probably a "buffer overflow" or some other kind of overrun in
the local variables of func2. In the usual processors, the stack
grows downward, and the local variables are allocated on the stack.
So the local variables of func2 are stored before the the local
variables of func1, and if you write beyond the bounds of the local
variables of func2, you can erase the frame pointers, the return
addresses and the local variables of the calling procedures.
The solution would be to debug func2.
--
__Pascal Bourguignon__
Thank you for quick reply for my query. It is not possible for me to
post code. It is a big application and lots of variables.
I will try to debug it according your suggestions. Please post me
some more suggestions if any.
Make sure that your debugger allows you to watch a memory location.
Once you choose change in what variable you want to watch for, point
your memory location to the address of that variable and step through
the 'func2' while watching what happens to the memory. Find what action
makes the memory contents go from what they were to 0xfd. Look at the
action and understand it.
V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask
"Sa***********@ gmail.com" <Sa***********@ gmail.comwrites :
Thank you for quick reply for my query. It is not possible for me to
post code. It is a big application and lots of variables.
I will try to debug it according your suggestions. Please post me
some more suggestions if any.
Well, given this kind of behavior (of your program), it might be very
useful for you to run it under valgrind. You will probably find a
lot of bugs with valgrind. http://valgrind.org/
--
__Pascal Bourguignon__ pj*@informatima go.com (Pascal J. Bourguignon) kirjutas:
"Sa***********@ gmail.com" <Sa***********@ gmail.comwrites :
>Thank you for quick reply for my query. It is not possible for me to
post code. It is a big application and lots of variables.
I will try to debug it according your suggestions. Please post me
some more suggestions if any.
Well, given this kind of behavior (of your program), it might be very
useful for you to run it under valgrind. You will probably find a
lot of bugs with valgrind.
http://valgrind.org/
Valgrind only runs on Linux (according to the info they give on the
page). I don't know what OP uses, but the value 0xfdfdfdfd looks like it
might be produced by Microsoft VC++ Debug build. If this is the case,
0xfd is used for no-mans land safety buffers before and after a user-
allocated object. If you are seeing this value in your data objects, you
have somehow corrupted your heap or accessing objects whose lifetime has
already ended earlier and have been overwritten by some other objects.
However, VC++ has a quite fine debugger, you can place a data breakpoint
to monitor a specific memory location as suggested already by somebody
else, and find out when and why it changes.
HTH
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