Expert: Ralph McArdell - 11/14/2010

Question
Hi,
I had previously asked you many questions. Thanx for response. I am new to the world of programing.

I was using Turbo C++ compiler 16 bit enviornment(windows Xp). But now found it inconvenient and now switched over to DevC++. Also I want to get the '.exe' file, which I think will be possible by using DevC++. Is it possible to get '.exe' file by using turboC?
Some of the portion of the program is given below-

#include<fstream>
#include<iostream>
#include<conio.h>
#include<stdlib.h>
#include<string>
#include<iomanip>
#include<stdio.h>
#include<limits>
#include<windows.h>

using namespace std;  
int main()
{
std::ofstream outfile;
outfile.open("WR_TEDs.DAT",ios::binary|ios::out);
if(!outfile)
  {
  cout<<endl<<"unable to open ";
  outfile.close();
  getch();
  }
  else
  outfile.close();

std::fstream infile("RD_TEDSs.DAT");
infile.open("RD_TEDs.DAT",ios::in|ios::out|ios::binary);
   if(!infile)
  {
  cout<<endl<<"unable to open file";
  infile.close();
  getch();
  }
  else
  infile.close();
getch();
}

IN CASE OF DevC++:
In this case, it shows no errors or warnings. The outfile "WR_TEDs.DAT" gets created and executed properly. The infile
"RD_TEDs.DAT" doesn't get created and it prints 'unable to open file' on screen as given in program. I have tried a lot but the infile is unable to get created while outfile gets created. Please help me on how to open a binary file in both the input and output modes in DevC++. (In the program later I also want to remove this file.)

IN CASE OF Turbo C:
above program gets executed properly without any error or warning, and both files get created.

-thankx.
abhijeet.

Answer
The differences you are seeing are differences between the probably pre ISO standard C++ IOStreams implementation used by the old 16-bit Borland C++ product (sometimes these are called "traditional IOStreams") and that of the more up to date and ISO C++ standard compliant C++ IOStreams implementation of the GNU C++ implementation used by DevC++ (the MinGW port see http://www.mingw.org/).

Your first obvious problem is that you have attempted to open the in/out file _twice_:

   std::fstream infile("RD_TEDSs.DAT");                        // create and attempt to open file
   infile.open("RD_TEDs.DAT",ios::in|ios::out|ios::binary);    // attempt to open file again

The first attempt to open the file during construction will attempt to open the file with the default std::fstream open modes of std::ios_base::in|std::ios_base::out (or, more conveniently for us std::ios::in | std::ios::out). This will _fail_ if the file RD_TEDSs.DAT does _not_ exist, as opening for reading requires the file to exist first. The second attempt to open the file will fail for the same reason.

If however the file RD_TEDSs.DAT did happen to exist for some reason then the first attempt will succeed and the second attempt fail - because the file is already open so the _operation_ fails. The file would however be open, from the initial open during construction. A file stream can be tested to see if it is connected to an open file using the is_open operation:

   if ( infile.is_open() )
   {
   // ...
   }

To open a file for input and output and creating the file if it does not exist we have to specify std::ios_base::trunc (or std::ios::trunc, or as you have a using namespace std directive in effect, just ios::trunc). This will of course truncate the contents of any existing file but will create the file if it does not already exist. So either do:

   std::fstream infile("RD_TEDSs.DAT",ios::in|ios::out|ios::trunc|ios::binary);

Or:

   std::fstream infile;
   infile.open("RD_TEDs.DAT",ios::in|ios::out|ios::trunc|ios::binary);

You can then check the stream is connected to an open file using the is_open() operation:

   if ( infile.is_open() )
   {
       std::cout << "infile opened OK.\n";
   }

You can check the stream state after the last operation is OK like so:

   if ( infile )
   {
       std::cout << "infile not in a bad or failed state.\n";
   }

Or conversely if it is not OK, as you were doing,

   if ( !infile )
   {
       std::cout << "infile is in a bad or failed state.\n";
   }


A stream is bad if it encountered an unrecoverable error. A stream is failed if the last operation failed but is recoverable - this is most commonly encountered when performing formatted input using the >> operator and the input characters are illegal for the format for the receiving type (e.g. non-digit characters other than - or + in integer input data).

The above test using !infile is equivalent to:

   if ( infile.fail() )
   {
       std::cout << "infile is in a bad or failed state.\n";
   }

The stream state testing member functions are:

  strm.eof()   -   returns true if end of file reached
  strm.fail()  -   returns true if there was a bad, fatal error or recoverable failure
  strm.bad()   -   returns true if there was a fatal error
  strm.good()  -   returns true if not bad, fail or eof

I also noticed that you are including many more header files than this piece of code requires. In particular do not include windows.h unless you are writing MS Windows specific code. In fact your code only required <fstream> and <iostream> and the non-standard <conio.h> for getch (all calls to which I commented out so I could build your code using the GNU compiler under Linux).

Also please pay attention to indentation and general code layout. The indentation of your code was all over the place making your code look very untidy and sloppy. It may not matter to the compiler but it does to us humans - well laid out code aids readability. In the same way I would hope you would want to look smart if you presented yourself socially it is polite and helpful to present your code in a smart and tidy fashion for the world to see, and of course shows you care enough to be bothered - if you cannot be bothered to present your code as well laid out and easy to get into as possible way why should anyone else bother to try to understand it if they do not have to (e.g. AllExpert volunteer question answerers like me)?

In any case I hope this helps.