error-handling-in-files.md

Error Handling Functions in Files

During file I/O operations, errors can occur due to any reason. Some of the reason are:

• A file on which we are trying to do a read/write operation may not exist.
• No availability of disk space to store data.
• Reading the file beyond the end-of-file.
• The file on which we are attempting a write operation may be protected.

So to handle these situations C++ provides few functions and flags which are defined in the 'istream' and 'ostream' classes. They are as followe:

• 'eof()' function and 'eofbit()' flag
• 'fail()' funciton and 'failbit()' flag
• bad()' function and 'badbit()' flag
• 'clear()' function
• 'good()' function

(i) 'eof()' funciton and 'eofbit' flag:

• The 'eof()' function returns true if end-of-file is encountered by the file pointer during a read operation and sets the 'eofbit' to true. Else the 'eof()' function returns false.
• Here's an example below explaining the same:

while(1)
{
   if(fin.eof())
      break;
   else
   {
      fin.read(&c, sizeof( c ));
      cout << c;
   }
}

(ii) 'fail()' funciton and 'failbit' flag:

• The 'fail()' function returns true and sets the 'failbit' flag to true if a file could not be opened for any of the reasons as mentioned before.
• Here's an exmaple below explaining the same:

do
{
   if(fin.fail())
   {
      cout << "Cannot open the file" << endl;
      break;
   }
   if(fin.eof())
      break;
   else
   {
      fin.read(&c, sizeof( c ));
   }
}while(1);

(iii) The 'bad()' function and 'badbit' flag:

• The 'bad()' function returns true adn sets the 'ba;bit' flag to true if any serious unrecoverable error has occurred.

(iv) The 'clear()' function:

• The 'clear()' function clears the bits set by the 'bad' function.

(v) The 'good()' function:

• The 'good()' function returns true if all the above functions turn false. It means that if 'good()' function returns true, then the file i/o operation has occurred without any error.