Segmentation Fault - Core Dumped.

Hi

i am running gcc under unix, when i compile the below source code and execute it under command mode, i get the required output. If the same executable is executed under cron, i am getting an error as "Segmentation Fault - Core Dumped". Could any one help me why i am getting this.

---source start---

#include <fstream>
#include <string>
#include <stdlib.h>
using namespace std;

int main(int argc, char* argv[]) {
  if ( argc != 2 ) {
   cout << endl << " Usage : " << argv[0] << " <userid>" << endl ;
   cout << " This will delete userid mails from your inbox" << endl ;
   exit(1) ;
  }
  string line ;
  char* usr = getlogin();
  char* inpath="/var/mail/";
  char* tmppath="/tmp/";
  char* inpfl = new char[strlen(usr)+strlen(inpath)+1];
  char* outfl = new char[strlen(usr)+strlen(tmppath)+1];
  strcpy(inpfl, inpath);
  strcat(inpfl, usr);
  strcpy(outfl, tmppath);
  strcat(outfl, usr);
  strcat(outfl, ".tmp");

  ifstream in(inpfl) ;
  ofstream out(outfl) ;
  int found = 0 ;

  while (getline(in,line)) {
   string findW(line) ;
   int strfound = findW.find("From ") ;
   if ( strfound == 0 ) {
      int tstfound = findW.find(string("From ") + argv[1]) ;
     if ( tstfound == 0 )
      found = 1;
     else
     {
      out << line << endl ;
      found = 0 ;
      }
    }
    else
    if ( found == 0 )
      out << line << endl  ;
  }

  char* mvstring = new char[strlen(outfl)+strlen(inpfl)+1];
  strcpy(mvstring,"mv ") ;
  strcat(mvstring,outfl) ;
  strcat(mvstring," ") ;
  strcat(mvstring,inpfl) ;
  system(mvstring) ;
}                                                                                                                                    

---source end---

Note : I doubt the reason to core error is that the system could not recognise the loginname when run under cron, if this is so how to overcome this, is there any way to get the loginname.

Sorry for long summary. helps appreciated.

--gsbabu