Fw: [techtalk] A SIGSEGV problem

[Ellen Venable]

here's an example:

I made a program called test.cc:
------------------------------------------------
#include <iostream.h>

main(){
 char * ptr;
  while(1){
// we'll print out whatever ptr points to (garbage)
// and then we'll increment ptr to move to the
// next memory location to be sure we eventually
// get outside of the memory belonging to our program
    cout <<ptr++;
  }
}
------------------------------------------------------
now compile it

>g++ -ansi -Wall -g test.cc

(the -g flag is for the debugger)

now run it

>./a.out


Hcccc(eeeec
c
c

Segmentation fault
                        
now run the debugger

>gdb a.out

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This GDB was configured as "i386-suse-linux-gnu"...
(gdb) run
Starting program: /home/ev/a.out 

Hcccc(eeeec
c
c

Program received signal SIGSEGV, Segmentation fault.
0x400487c7 in ostream::operator<< (this=0x8049998, 
    s=0x804a000 <Address 0x804a000 out of bounds>) at iostream.cc:823
823     iostream.cc: No such file or directory.
(gdb) backtrace
#0  0x400487c7 in ostream::operator<< (this=0x8049998, 
    s=0x804a000 <Address 0x804a000 out of bounds>) at iostream.cc:823
#1  0x80487e1 in main () at test.cc:10
(gdb) quit
The program is running.  Exit anyway? (y or n) y
-----------------------------------------------

Under windows, this printed out stuff for quite a while and
then windows did notice that we went out of bounds
(got "Access Violation" error)