Thread: simple i/o error that I cannot solve

So, I am writing my very own binary xor-based encryptor. Grand. I am running into a very strange problem with ifstream.
I'll open the file without error, and then use istream::getline(). Getline() functions normally, but subsequent calls to fail() (on the file stream) are true. Subsequent calls to get() (on the file stream) return -1. Strangely, subsequent calls to getline() (even after fail() is true) function normally. What is going on? Additionally, the end of the file has NOT been reached. Here's a sample of the problematic code:

Code:

 ios::iostate xor_file::xor_open(string input_path)
{
 char* buffer = new char[25];//DEBUG
 string sample;
 encoded = decoded = xor_open_switch = false;
                          
 reader.open(input_path.c_str(),ios::binary);    //open the file
 if(reader.fail())                               //check for failure
 {
  reader.close(); 
  return ios::failbit;
 }         
                   //Didn't fail....
 xor_open_switch = true;                         //we're open for business (until close()is called)
 
 if(reader.fail()) cout << "something's wrong BEFORE FIRST GETLINE. xor_open()" << endl; //DEBUG
 reader.getline(buffer,25,'@');                    //sample for c:\windows\desktop\primes.txt
 if(reader.fail()) cout << "something's wrong AFTER FIRST GETLINE. xor_open()" << endl; //DEBUG
 sample = buffer;                                  //make it a string DEBUG
 cout << "open()'s \"sample\": " << sample << endl;      //DEBUG

. . . . . . . (in same function)

Code:

cout << "Some get(): ";
 for(int z = 0; z < 10; z++) cout << reader.get();    //DEBUG
   cout << boolalpha << "reader.eof(): " << reader.eof() << endl; //DEBUG

The output of this code is:
something's wrong AFTER FIRST GETLINE. xor_open()
open()'s "sample": 25 characters of good health
Some get(): -1-1-1-1-1-1-1-1-1-1-1-1
reader.eof(): false

"25 characters of good health" was a noncontextual example.my bad. Allow me to elaborate:
class xor_file is an object meant to control i/o, encryption, decryption and storage of passwords, keys, etc.
xor_file::xor_open() would be the first function called by an xor_file object.
1. Open file
2. See if the file has already been encrypted by the program
2a. If it has been encoded already, read in data regarding the password and key so that it might be decoded later.
2b. If not, simply set the necessary flags to denote an unencrypted file.
3. Return

Now, I had found that after calling the function, I was getting trouble in another function xor_file::xor_encode(). I found that the issue went all the way back to xor_open(), and so I pasted some code from the former function to see what was up. In my code, //DEBUG is beside any line that was added for debugging.
Here is the whole function:

Code:

ios::iostate xor_file::xor_open(string input_path)
{
 char* buffer = new char[25];
 string sample;
 encoded = decoded = xor_open_switch = false;   //member switches
                          
 reader.open(input_path.c_str(),ios::binary);    //open the file
 if(reader.fail())                               //check for failure
 {                                                  //yes, I could have just done if(!reader)
  reader.close(); 
  return ios::failbit;
 }         
                   //Didn't fail....
 xor_open_switch = true;                         
 
 if(reader.fail()) cout << "something's wrong BEFORE FIRST GETLINE. xor_open()" << endl; //DEBUG
 reader.getline(buffer,25,'@');                    //sample for c:\windows\desktop\primes.txt
 if(reader.fail()) cout << "something's wrong AFTER FIRST GETLINE. xor_open()" << endl; //DEBUG
 sample = buffer;                                  //make it a string DEBUG
 cout << "open()'s \"sample\": " << sample << endl;      //DEBUG
 
 if(sample == "XOR_CODEC_ENCRYPTED_FILE")   //This file is already encrtypted
 {
  encoded = true;
  encoded_path = input_path;                             //set the xor_file path to the valid path
  
  getline(reader,sample,'@');                   //sample for password
  cout << "Password (encrypted): " << sample << endl;        //DEBUG
  for(int x = 0; x < sample.size(); x++) sample[x] -= static_cast<char>(1); //TODO: use better algorithm
  cout << "Password (decrypted): " << sample << endl;        //DEBUG
  password = sample;
  
  getline(reader,sample,'@');                   //sample for key
  cout << "Key: " << sample << endl;
  key = sample;
 }
 else                                       //This file is not encrypted
 {
  decoded = true;
  decoded_path = input_path;                             //set the xor_file path to the valid path
  //reader.seekg(1,ios::beg);                              //reset reader for encoding later
   for(int z = 0; z < 10; z++) cout << reader.get();    //DEBUG
   cout << boolalpha << "reader.eof(): " << reader.eof() << endl; //DEBUG
 }

Here is the input file (text):

This is a text-only test just to see if the damn
thing works. Of course, as I write this, I haven't
even compiled all of my new functions. It is likely
that I will get tons of error and not even use
this test file for quite a while. Still, I'm not
discouraged. (quite more than 25 chars)

and the output:

Please input path to file.
c:\windows\desktop\input.txt
something's wrong AFTER FIRST GETLINE. xor_open()
open()'s "sample": This is a text-only test
-1-1-1-1-1-1-1-1-1-1reader.eof(): false

Thank you for your help.

Well, it's strange, but the getline function does set the stream in the error state for some reason after the first read. (The string getline works well.) Once the file stream is in the error state, the next reads won't make any sense, so don't worry about the get() calls. The problem is with the first getline().

(An easier way would probably be to read in the whole file at once, and then parse the "metadata".)

Edit: here's my test (DevC++ 4.9.9.2 & MingW)

Code:

#include <iostream>
#include <fstream>
#include <string>

#define STRINGVERSION 1 //use 0 to see char[] version

int main()
{
    std::ifstream file("test.txt", std::ios::binary);
    #if STRINGVERSION
        std::string buffer;
    #else
        char buffer[25];
    #endif
    if (file) {
        #if STRINGVERSION
            while (std::getline(file, buffer, '@'))
        #else
            while (file.getline(buffer, 25, '@'))
        #endif
        {
            std::cout << buffer << '\n' << "Good: " << file.good()
                      << '\n' << "Fail: " << file.fail()
                      << '\n' << "Bad: " << file.bad()
                      << '\n' << "Eof: " << file.eof() << std::endl;
        }
    }
    else {
        std::cout << "Couldn't open file" << '\n';
    }
    std::cin.get();
}

/*(test.txt) =
This is a text-only test@just to see if the damn@
thing works. Of course, as I write this, I haven't
even compiled all of my new functions. It is likely
that I will get tons of error and not even use
this test file for quite a while. Still, I'm not
discouraged. (quite more than 25 chars)
*/

The string version works properly: it reads the file in 3 chunks and discards the delimiters.
In char version the filestream stays good until it meets the delimiter in the 25 characters, otherwise getline makes !file and the loop exits (first 2 chunks are printed in the loop).

I've never used getline with char* buffer before, but I'd rather go with the string version.

OK, found out what's the problem in this thread. See post #4.

Code:

#include <iostream>
#include <fstream>
const char BUFFER_SIZE = 25;
int main()
{
    std::ifstream file("test.txt", std::ios::binary);
    char buffer[BUFFER_SIZE];
    if (!file) return 1;
    
    //while any characters successfully read (gcount())
    while (file.getline(buffer, BUFFER_SIZE, '@').gcount()) {
        //clear the fail bit
        file.clear(file.rdstate() & ~std::ios::failbit);
        std::cout << buffer << '\n' << "Good: " << file.good()
                  << '\n' << "Fail: " << file.fail()
                  << '\n' << "Bad: " << file.bad()
                  << '\n' << "Eof: " << file.eof() << std::endl;
        /*clear the buffer
        It may not be filled entirely and that would leave
        parts of it from previous getline()s.
        */ 
        for (int i = 0; i < BUFFER_SIZE; i++)
            buffer[i] = 0;
    }
    std::cin.get();
}

Also note that file.getline(buffer, n, delimiter) reads n-1 characters to append the zero-terminator.

Thank you very much for your help. However, I will choose not to read in the entire file and then work with it in memory, because (this application being an encryptor) I might be dealing with obscenely large files. Anyways, thanks again.

Oh, one more thing. Suppose I want to read data into a string as usual:

Code:

istream::getline(file_stream,std_string_obj,delim_char);

But I also wanted to place a cap on the number of chars to be read. So far I haven't found such a version of the function. Does one exist?

Yes, for the acctual encryption/decryption everything would be cstrings. I just wanted to use std::strings for the file header stuff to make it easier. Easier it is not.