segmentation fault when allocating memory with new or malloc

[Tobias Kretz]

Hi,

thanks for all the help,
since the problem looked so weired at first I will describe what went
wrong here. Maybe it´ll be useful for someone else someday:

Indeed the problem lay at some other point in the program.
I had a structure which itself contained pointers used as starting
points for a dynamical arrays.
I had two dynamical arrays (let´s say p1 and p2) of that structure. I
did allocate the memory (p1= new ...; p2=new ...) for those but with one
of them I forgot allocating the memory for the dyn. ar.s within the 
structure (p2[int2].px=new...). Sth. like p1[int1]=p2[int2] then 
corrupted the memory.

Thanks again,

Tobias



lrtaylor@micron.com wrote:
> Have you tried looking at a stack trace to see where your program is actually crashing?  With the core file, you can even look at the value of variables, etc.  Whenever I get a segmentation fault, the first thing I do is look at the stack trace to see where it happened.
> 
> If you've never looked at a stack trace before, then you should probably take a look at the manual for GDB.  They have a section on examining the stack.  You'll also need to make sure that your programs are generating a core file when they crash.  RedHat seems to have turned this off by default, but you can reenable it in the current shell using the ulimit command:
> 
> ulimit -c unlimited
> 
> Otherwise, I concur with what another poster said - you've probably corrupted memory before ever getting to this point, and this is just bringing the problem out.  I would go over your code with a fine-toothed comb and look for any problems with pointers.
> 
> Good luck,
> Lyle
> 
> -----Original Message-----
> From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org]On
> Behalf Of Tobias Kretz
> Sent: Tuesday, January 13, 2004 3:32 AM
> To: gcc-help@gcc.gnu.org
> Subject: segmentation fault when allocating memory with new or malloc
> 
> 
> Hi,
> 
> allocating memory with one of these lines:
> 
> pl=(list*)malloc((v)*sizeof(list));
> or
> list*pl; pl=new list[v];
> 
> causes the program to be terminated by a segmentation fault.
> v is an integer that equals e.g. 7 in my test runs (thus far from 
> throwing a bad_alloc)
> 
> and list is trivially:
>   struct list{
>   	     int x;
> 	     int y;
> 	  double d;
> 	    };
> 
> Replacing the variable v by a constant value does not improve the 
> situation.
> Also:
>   cout << "A\n";
>   try {pl=new list[v];}
>   catch(bad_alloc) {cerr<< "not enough memory\n";}
>   cout << "B\n";
> results in the output:
> A
> Segmentation fault
> 
> Additionally weird is that omitting the memory allocation
> makes the program run further. Yet it crashes with a seg fault.
> when trying to set up an outfile stream:
> bmpofstream image("floor.bmp",xmax,ymax);
> later in the program. The rest of the program contains datastructures 
> for which I allcoate some 100kB memory (with new).
> 
> I use g++, gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)
> 
> Regards,
> ToK
> 
> 

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