Re: ifstream open function fails
Christian wrote:
#include "fstream"
#include "iostream"
Use
<fstream>
<iostream>
, i.e. with angled brackets.
char fileName[80];
char buffer[255];
This is typically wrong, because it tends to cause buffer overflows.
cout << "Please re-enter the file name: ";
cin >> fileName;
This is surely wrong. If I enter
"C:\Dokumente und Einstellungen\u_eckhardt\Eigene Dateien\Development\MPVL
examples\file zum testen.ascii"
, what do you think this will become within 'fileName'? There are two
assumptions that are wrong:
1. filenames are less than 80 characters in length
2. filenames contain no whitespace
#include <string>
...
std::string filename;
getline( std::cin, filename);
This only assumes that filenames contain no linebreaks but doesn't assume
any length limits. You then open the file like this:
std::ifstream in(filename.c_str());
ifstream fin(fileName);
if (fin) // already exists?
{
//read file content...
}
fin.close();
[...]
fin.open(fileName); // reassign existing fin object!
// here are my proofs with different functions: you can't see
// that they're not all FALSE
// fin.fail() TRUE
// fin.bad() FALSE
// fin.eof() TRUE
// can't open file anynmore!!
Note: after reading the last character, the attempt is made to read another
one and that sets the failbit and the eofbit, hence above state.
Others already told you that you need to call clear() on the stream.
However, for your understanding, the idea is that none of these bits are
ever reset by a stream operation except by the programmer explicitly
calling clear(). Yes, it's surprising at first that fstream's open()
doesn't do that implicitly, but at least the operation is consistent
throughout all stream classes.
Uli