Integer Array Size Problem

Integer Array Size Problem

[Digvijoy Chatterjee]

Hi ,
I was trying to test algorithms with huge int arrays when i started
getting segfaults..here is a simple program which emulates this
behaviour...
Each time i run this program , it segfaults , This might be very naive
..but can anyone help me with what I am missing here ?

static const int N=10000000;
int main()
{
int c, i[N];
for (c=0;c<N ; c++ )
i[c]=c;
}

Thanks
Digz

Re: Integer Array Size Problem

[Digvijoy Chatterjee]

Thanks,
the heap allocation code (malloc)  ran without a problem..
so does a stack overflow mean ,that the stack can grow only to a
maximum size in the memory ??..who sets this ,and how does one change
this..
10,000,000 integers seems very little to overflow the stack.

-Digz

  On 12/3/06, Blake Huff <stangmechanic@gmail.com> wrote:
> I believe this is what people refer to as stack overflow.  Take a look at
> allocating the memory with something like malloc, i.e.,
>
> int *i = (int *) malloc(N * sizeof(int));
>
>
>
>
>
> Blake Huff
> stangmechanic@gmail.com
>
> "I'd like to take this opportunity to thank my cat for letting me live
> here."
>
>
> On Dec 3, 2006, at 12:56 PM, Digvijoy Chatterjee wrote:
>
> Hi ,
> I was trying to test algorithms with huge int arrays when i started
> getting segfaults..here is a simple program which emulates this
> behaviour...
> Each time i run this program , it segfaults , This might be very naive
> ..but can anyone help me with what I am missing here ?
>
> static const int N=10000000;
> int main()
> {
> int c, i[N];
> for (c=0;c<N ; c++ )
> i[c]=c;
> }
>
> Thanks
> Digz
>

Re: Integer Array Size Problem

[Blake Huff]

Digz:

Stack size is set by the OS, and there are typically ways to adjust  
this in each OS. This is the part where we'll get berated for being  
off topic, as this isn't a GCC question, but rather one appropriate  
for a general programming list, or for one about your OS.

The default stack size for some OS's (like Mac OS X) is 8 megabytes.  
Ten million integers at 4 bytes each would take 40 million bytes ~ 40  
megabytes, and overflow the stack.

If you're interested in learning more, I suggest doing Google  
searches for stack size/allocation, etc..   However, I think the  
preferred technique is to malloc large arrays, in the event that your  
code is moved from a machine/OS with a large stack to a machine with  
an unacceptably small stack, etc.

Blake

"When the going gets tough, the tough get aeronautical."-Howling Mad  
Murdoch


On Dec 3, 2006, at 1:18 PM, Digvijoy Chatterjee wrote:

> Thanks,
> the heap allocation code (malloc)  ran without a problem..
> so does a stack overflow mean ,that the stack can grow only to a
> maximum size in the memory ??..who sets this ,and how does one change
> this..
> 10,000,000 integers seems very little to overflow the stack.
>
> -Digz
>
>  On 12/3/06, Blake Huff <stangmechanic@gmail.com> wrote:
>> I believe this is what people refer to as stack overflow.  Take a  
>> look at
>> allocating the memory with something like malloc, i.e.,
>>
>> int *i = (int *) malloc(N * sizeof(int));
>>
>>
>>
>>
>>
>> Blake Huff
>> stangmechanic@gmail.com
>>
>> "I'd like to take this opportunity to thank my cat for letting me  
>> live
>> here."
>>
>>
>> On Dec 3, 2006, at 12:56 PM, Digvijoy Chatterjee wrote:
>>
>> Hi ,
>> I was trying to test algorithms with huge int arrays when i started
>> getting segfaults..here is a simple program which emulates this
>> behaviour...
>> Each time i run this program , it segfaults , This might be very  
>> naive
>> ..but can anyone help me with what I am missing here ?
>>
>> static const int N=10000000;
>> int main()
>> {
>> int c, i[N];
>> for (c=0;c<N ; c++ )
>> i[c]=c;
>> }
>>
>> Thanks
>> Digz
>>

Fwd: Integer Array Size Problem

[Dima Sorkin]

On 12/3/06, Digvijoy Chatterjee wrote:
> Thanks,
> the heap allocation code (malloc)  ran without a problem..
> so does a stack overflow mean ,that the stack can grow only to a
> maximum size in the memory ??..who sets this ,and how does one change
> this..
ulimit

> 10,000,000 integers seems very little to overflow the stack.
It is a least 40MB which seems unreasonably high. See below on my
machine (in kB):

bash-3.00$ ulimit -s
10240


Regards,
 Dima.

Re: Fwd: Integer Array Size Problem

[Tim Prince]

Dima Sorkin wrote:
> On 12/3/06, Digvijoy Chatterjee wrote:
>> Thanks,
>> the heap allocation code (malloc)  ran without a problem..
>> so does a stack overflow mean ,that the stack can grow only to a
>> maximum size in the memory ??..who sets this ,and how does one change
>> this..
> ulimit
> 
>> 10,000,000 integers seems very little to overflow the stack.
> It is a least 40MB which seems unreasonably high. See below on my
> machine (in kB):
> 
> bash-3.00$ ulimit -s
> 10240

On my current (32-bit Windows) platform:
$ ulimit -s
2032

So, if you intend portable code, you surely can't count on availability 
of larger stacks. 1MB per thread used to be a typical hard limit for 
static linked 32-bit linux libraries.  The 1MB per thread stack thing 
was ubiquitous enough to require hardware level changes since the 
original P4, which had cache mapping conflicts ("64k aliasing") between 
stacks at 1MB intervals, as implemented by the most popular C platform. 
  The hardware fix still is vulnerable to problems with stacks at 
intervals of multiples of 8MB, if I understand the situation correctly.
Standard C, of course, says nothing about stacks and their sizes, but it 
doesn't say that you can ignore limitations of common platforms.

Re: Integer Array Size Problem

[Tim Prince]

Digvijoy Chatterjee wrote:
> Hi ,
> I was trying to test algorithms with huge int arrays when i started
> getting segfaults..here is a simple program which emulates this
> behaviour...
> Each time i run this program , it segfaults , This might be very naive
> ..but can anyone help me with what I am missing here ?
> 
> static const int N=10000000;
> int main()
> {
> int c, i[N];
> for (c=0;c<N ; c++ )
> i[c]=c;
> }
> 
Evidently, this depends on platform (e.g. 32- or 64-bit), possibly on 
compiler options (e.g. mc-model) or shell settings (e.g. ulimit), none 
of which you have divulged. Not giving such information doesn't make it 
On Topic.