I just finish writing LAB2 with no errors when compiling, but once i run
it, i get "segmentati on fault".. i don't know what is wrong, can anyoen
tell me what it means and how i can fix it? thx!
Nov 14 '05
21  8310 
"Jeremy Yallop" <je****@jdyallo p.freeserve.co. uk> wrote in message
news:sl******** ***********@heh e.cl.cam.ac.uk. .. Peter Pichler wrote: "Jeremy Yallop" <je****@jdyallo p.freeserve.co. uk> wrote in message
news:sl******** ***********@heh e.cl.cam.ac.uk. .. Peter Pichler wrote:
>
> Yes. The statistics show that 100% of segmentation faults are caused
by > derefencing an invalid pointer.
$ cat recurse.c
int main() { return main(); }
$ gcc -ansi -pedantic recurse.c
$ ./a.out
Segmentation fault
Your example involves dereferencing an invalid pointer.
Really? At which point, and for what reason, does the pointer become
invalid?
Isn't calling a function dereferencing a function pointer?
This is a genuine question, I am not so sure any more.
Peter
Peter Pichler wrote: "Jeremy Yallop" <je****@jdyallo p.freeserve.co. uk> wrote in message
news:sl******** ***********@heh e.cl.cam.ac.uk. .. Peter Pichler wrote: > "Jeremy Yallop" <je****@jdyallo p.freeserve.co. uk> wrote in message
> news:sl******** ***********@heh e.cl.cam.ac.uk. ..
>> Peter Pichler wrote:
>> >
>> > Yes. The statistics show that 100% of segmentation faults are caused by >> > derefencing an invalid pointer.
>>
>> $ cat recurse.c
>> int main() { return main(); }
>> $ gcc -ansi -pedantic recurse.c
>> $ ./a.out
>> Segmentation fault
>
> Your example involves dereferencing an invalid pointer.
Really? At which point, and for what reason, does the pointer become
invalid?
Isn't calling a function dereferencing a function pointer?
This is a genuine question, I am not so sure any more.
I believe you're correct. (Since, I am watching my mouth as far as
interpreting the standard for the general public goes, I won't assert that
you're correct :-)
From 6.3.2.1:
4 A function designator is an expression that has function type. Except when
it is the operand of the sizeof operator54) or the unary & operator, a
function designator with type "function returning type" is converted to an
expression that has type "pointer to function returning type".
Further, 6.5.2.2 Function Calls:
1 The expression that denotes the called function77) shall have type pointer
to function returning void or returning an object type other than an array
type.
77) Most often, this is the result of converting an identifier that is a
function designator.
-nrk.
Peter
--
Remove devnull for email
Peter Pichler wrote:
"Jeremy Yallop" <je****@jdyallo p.freeserve.co. uk> wrote in message
news:sl******** ***********@heh e.cl.cam.ac.uk. .. Peter Pichler wrote: "Jeremy Yallop" <je****@jdyallo p.freeserve.co. uk> wrote in message
news:sl******** ***********@heh e.cl.cam.ac.uk. ..
> Peter Pichler wrote:
> >
> > Yes. The statistics show that 100% of segmentation faults are caused by> > derefencing an invalid pointer.
>
> $ cat recurse.c
> int main() { return main(); }
> $ gcc -ansi -pedantic recurse.c
> $ ./a.out
> Segmentation fault
Your example involves dereferencing an invalid pointer.
Really? At which point, and for what reason, does the pointer become
invalid?
Isn't calling a function dereferencing a function pointer?
This is a genuine question, I am not so sure any more.
The second appearance of `main' is in fact a function
pointer, and the `()' function-call operator uses that pointer
value to determine what function to invoke. Whether this use
constitutes a "dereferenc e" is unclear -- the Standard neither
defines nor uses the word.
At any rate, the function pointer value `main' remains
valid for the life of the program. Thus, the call is not
"dereferenc ing an invalid pointer" because the pointer is
not invalid.
-- Er*********@sun .com
On 6 Feb 2004 22:22:58 GMT, in comp.lang.c , Jeremy Yallop
<je****@jdyallo p.freeserve.co. uk> wrote: Peter Pichler wrote: "Jeremy Yallop" <je****@jdyallo p.freeserve.co. uk> wrote in message
news:sl******** ***********@heh e.cl.cam.ac.uk. .. Peter Pichler wrote:
>
> Yes. The statistics show that 100% of segmentation faults are caused by
> derefencing an invalid pointer.
$ cat recurse.c
int main() { return main(); }
$ gcc -ansi -pedantic recurse.c
$ ./a.out
Segmentation fault
Your example involves dereferencing an invalid pointer.
Really? At which point, and for what reason, does the pointer become
invalid?
when you run out of memory .
--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.angelfire.c om/ms3/bchambless0/welcome_to_clc. html>
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Martin Ambuhl <ma*****@earthl ink.net> wrote in message news:<DT******* ************@ne wsread1.news.at l.earthlink.net >... us**@domain.inv alid wrote:
I just finish writing LAB2 with no errors when compiling, but once i run
it, i get "segmentati on fault".. i don't know what is wrong, can anyoen
tell me what it means and how i can fix it? thx!
Stop dereferencing invalid pointers.
What happened to our OTNs (off-topic Nazis). Why aren't they stomping
the guts out of these people saying "segmentati on ain't in our
bible^Wstandard !" :-)
MSG (no, I'm not an OTN) us**@domain.inv alid wrote: I just finish writing LAB2 with no errors when compiling
but once i run it, I get "segmentati on fault".
I don't know what is wrong,
Can anyone tell me what it means and how I can fix it?
Your program is attempting to reference memory
which doesn't belong to it.
You probably have an array index which is "out-of-bounds".
Use your debugger. If you don't have a debugger or know how to use it,
you can insert statements to print diagnostic messages
fprintf(stderr, "Got to this point in the program!\n"); fflush(stderr);
Put the first one smack dab in the middle of your code.
If you get the "segmentati on fault" before the diagnostic message
you know that the error is before the print statement and
the error is after the print statement
if you get the diagnostic message before the "segmentati on fault".
A short binary search usually locates the error quickly.
Jeremy Yallop wrote: Peter Pichler wrote: "Jeremy Yallop" <je****@jdyallo p.freeserve.co. uk> wrote Peter Pichler wrote:
>
> Yes. The statistics show that 100% of segmentation faults
> are caused by derefencing an invalid pointer.
$ cat recurse.c
int main() { return main(); }
$ gcc -ansi -pedantic recurse.c
$ ./a.out
Segmentation fault
Your example involves dereferencing an invalid pointer.
Really? At which point, and for what reason, does the pointer
become invalid?
Also, what pointer? To make sure, add void in "int main(void)"
--
Chuck F (cb********@yah oo.com) (cb********@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!
Eric Sosman wrote: Peter Pichler wrote: "Jeremy Yallop" <je****@jdyallo p.freeserve.co. uk> wrote Peter Pichler wrote:
> "Jeremy Yallop" <je****@jdyallo p.freeserve.co. uk> wrote
>> Peter Pichler wrote:
>> >
>> > Yes. The statistics show that 100% of segmentation faults
>> > are caused by derefencing an invalid pointer.
>>
>> $ cat recurse.c
>> int main() { return main(); }
>> $ gcc -ansi -pedantic recurse.c
>> $ ./a.out
>> Segmentation fault
>
> Your example involves dereferencing an invalid pointer.
Really? At which point, and for what reason, does the
pointer become invalid?
Isn't calling a function dereferencing a function pointer?
This is a genuine question, I am not so sure any more.
The second appearance of `main' is in fact a function
pointer, and the `()' function-call operator uses that pointer
value to determine what function to invoke. Whether this use
constitutes a "dereferenc e" is unclear -- the Standard neither
defines nor uses the word.
At any rate, the function pointer value `main' remains
valid for the life of the program. Thus, the call is not
"dereferenc ing an invalid pointer" because the pointer is
not invalid.
I was going to be a smart-ass and point out that compiling with
gcc -O2 did not generate the segment fault, because of tail
recursion optimization. Luckily I tried it first, and found that
gcc does NOT optimize this one. Must be a feature, couldn't
possibly be a bug.
--
Chuck F (cb********@yah oo.com) (cb********@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!
"Emmanuel Delahaye" <em**********@n oos.fr> wrote in message
news:Xn******** *************** ****@212.27.42. 68... In 'comp.lang.c', "E. Robert Tisdale" <E.************ **@jpl.nasa.gov >
wrote: fprintf(stderr, "Got to this point in the program!\n"); fflush(stderr);
I'm not sure thar stderr is buffered, hence the fflush() seems redunant.
Also, the line is terminated by a '\n', that makes the fflush() twice
redundant. What would be more informative would have been to add smart
information like the file name and the line in the file:
fprintf (stderr, "Got to here %s:%d in the program!\n", __FILE__,
__LINE__);
A nitpick here is that __LINE__ is not guaranteed to have int type.
--
Peter This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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