istream bug

[Robert Schweikert <rjschwei at mindspring dot com>]

When using the "ios::nocreate" opening mode on an istream the file
pointer moves to the end of the file which causes the read with the
stream operator ">>" to fail. I realize that using "ios::nocreate" on an
istream doesn't make a whole lot of sense, however, I think the compiler
should either ignore this opening mode on the istream or issue a warning
or error message. Putting the file pointer to the end of the file
produces behavior that is hard to track down.

The attached file illustrates the problem.

-> g++ -o strTestNb  strTest.C
-> ./strTestNb
First Flag: 0
Second Flag: 1
Third Flag: 0
This is buffer: Assembly-1
This is n: 1
This is i: 0
->

-> g++ -o strTest -DDEMOBUG strTest.C
-> ./strTest
This is i: 66267
This is i: 66268
This is i: 66269
This is i: 66270
This is i: 66271
This is i: 66272
This is i: 66273

This is an endless loop.

A fix is appreciated.

Thanks,
Robert


--
Robert Schweikert                      MAY THE SOURCE BE WITH YOU
rjschwei@mindspring.com                         LINUX


#include <iostream.h>
#include <fstream.h>



int main(void)
{
#if defined(DEMOBUG)
  ifstream input("strTest.prt", ios::nocreate);
#else
  ifstream input("strTest.prt");
#endif

  int flag;
  int n;
  int i;
  char tail[132], buffer[132];

  input >> flag;
  cout << "First Flag: " << flag << endl;
  input >> flag;
  cout << "Second Flag: " << flag << endl;
  input >> flag;
  cout << "Third Flag: " << flag << endl;

  input.getline(tail, 132); //Probably reads the end of the third line in the 
                            //file
  input.getline(buffer, 132);
  cout << "This is buffer: " << buffer << endl;

  input >> n;
  cout << "This is n: " << n << endl;

  for ( i =  0; i < n; i++) {
    cout << "This is i: " << i << endl;
  }

  return 1;
}
0
1
0
Assembly-1
1