occasional stackdump created and errors on program run.

[gcampton]

I'm having occasional errors when testing my program, I'm not quite sure. When this error occurs creates stackdump then will continue to produce the same error until I delete the stackdump.
only thing I could find on stackdump was: http://www.cplusplus.com/forum/general/4282/
which was completely useless. What is a stackdump?
Unfortunately the error didn't point to any specific line being it was exec, which is usually what I read when looking at errors it said something about char * std:: alloc etc..
I didn't quite get it .... hit the enter key too soon and ended up back in VI, and unfortunately being that I was using VI opening shell, when I quit to go check the error again it had scrolled off the term. I have tried to reproduce the error but it is not comming up at the moment, I assume I will get it again sooner or later I hope so i can try and figure out what is going on. There is only 1 if statement that it seemed to happen on a few times.
This is my code:

#include "header.h"

#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;

int main(int argc,char *argv[])
{
  int row=1;
  string iparam="";
  string oparam="";
  string usage="Usage: -i \"input_file\" -o \"output_file\"";

  // check if args have been supplied
  if (argc<=1)
  {
    cerr << usage << endl;
    exit(1);
  }
  // check switches
  else if (argv[1][0] != '-')
  {
    cerr << "invalid switch: " << argv[1] << endl;
    cerr << usage << endl;
    exit(1);
  }
  // stick in/out elements in string iparam/oparam
  while ((row<argc)&&(argv[row][0]=='-'))
  {
    string sw = argv[row];
    if (sw =="-i")
    {
      row++;
      iparam=argv[row];
    }
    else if (sw=="-o")
    {
      row++;
      oparam=argv[row];
    }
    else 
    {
      cerr << "unknown switch: " << argv[row] << endl;
      cerr << usage << endl;
      exit(1);
    }
    row++;
  }
  // check for duplicate filenames
  if (iparam==oparam)
  {
    cerr << "Duplicates found, use unique files." << endl;
    cerr << usage << endl;
    exit(1);
  }
  // this is the "if" i introduced that started giving me the errors
  // I had the previous code working and tested multiple times
  // before implementing this next conditional.

  // exit on more args than required:--
  if (argv[5][0]!=0)
  {
    cerr << "Too many args." << endl;
    cerr << usage << endl;
    exit(1);
  }

  // start app:
  StringSort ss(iparam,oparam);
  ss.runApp();
}

The bottom if or possibly the creating of StringSort object most likely causes, I don't think it would be the object because at the moment all it is taking iparam and oparam as constructor args and setting them, with a couple cout test statements in constructor, setters, and runApp...

I'll post back if I come across the error again, I just don't want to submit this knowing the code may be flawed, something I may be overlooking...

Thanks for reading so far.

[gcampton]

ok got it again i tried this on another computer using cygwin I commented out the include header and lines 70,71 compiled fine then I ran the exe as:

./a -i iinnnn -o ouuttttttt
16 [main] a 3704 _cygtls::handle_exceptions: Error while dumping state<probably corrupted stack>
segmentation fault (core dumped)

[writetonsharma]

debug the core using gdb and you will know where you got the exception.
if its a release binary, compile it with -g option and you can debug the core.
syntax:
gdb binary_name core

try it.

[gcampton]

ok I have never used this before but gave it a shot,
running the exe with args ::

[New thread 5532.0x1794]
(no debugging symbols found)
(...)
(...)
(...)
[New thread 5532.0x12e0]
(no debugging symbols found)
(...)
(...)
(...)
Program recieved signal SIGSEGV, Segmentation fault.
0x004016a9 in ?? ()   
(gdb)  

now compile using -ggdb flag
now that's useful :D thanks a bunch, so now that gdb has confirmed that what I thought was correct, can I say now change this to if *argc>=5 and retest etc, and it should tell me if successful yea?

Program recieved signal SIGSEGV, seg fault.
0z092131 in main (argc=5, argv=0xde2178) at a2Main.cpp:62
62    if (argv[5][0]!=0)

Also in the manual it doesn't talk much about debugging symbols, is there a better resource to look up how to use debugging symbols in code?

[gcampton]

I'm wondering why was the comparison against 0 throwing this seg fault?
I'm pretty sure i tried comparing to != NULL but it told me that it had to be an int which is why I changed to 0... doesn't matter too much anyway argc>5 is essentially the same.

[helios]

You're doing it wrong. You're not supposed to check argv[i][0]. If you do that, the [0] dereferences the pointer and you get a segmentation fault when i==argc. You're supposed to check argv[i].

[gcampton]

line 29: while ((row<argc)&&(argv[row][0]=='-')) is also going to cause this error?
I did read up on pointers before this, but assumed from what I read you can still treat them much like arrays, but I'm not quite sure what you mean....
are you saying that comparing [i][j] to 0 will be comparing against memory address?

[firedraco]

If you are accessing element [i][j] of an array, it means you are still dereferencing the 2nd pointer (to get the j-th element), but if that pointer is NULL, then you can't deference it.

[gcampton]

ah ok thanks.

[helios]

Shit, I forgot to click the submit button. Oh, well.