Thread: Binary file I/O

Why doesn't this program make a carbon copy? The output file is smaller than its counterpart and does not function.

Code:

#include <cstdlib>
#include <iostream>
#include <fstream>
using namespace std;

int main(int argc, char *argv[])
{
    unsigned long int x = 0;
    unsigned char buffer;
    ifstream reader("C:\\windows\\desktop\\1.jpg", ios::in | ios::binary);
    ofstream writer("C:\\windows\\desktop\\1_out.jpg", ios::out | ios::binary);
    if(reader.fail())
    {cout << "Failed to open file" << endl; return 1;}
    if(writer.fail())
    {cout << "Failed to open write stream" << endl; return 1;}
    
    while(!reader.eof())
    {
     reader >> buffer;
     if(x < 100) cout << buffer;
     writer << buffer;
     x++;
    }
    cout << x << endl;
    reader.close();
    writer.close();
    
    system("PAUSE");
    return EXIT_SUCCESS;
}

>while(!reader.eof())
That's one of your problems. The FAQ will explain why.

I think you need to be using the read and write function, because you are doing binary (i.e. unformatted) I/O. So, I suggest:

Code:

#include <cstdlib>
#include <iostream>
#include <fstream>
using namespace std;

int main(int argc, char *argv[])
{
    char buffer;
    ifstream reader("file1.jpg", ios::in | ios::binary);
    ofstream writer("file2.jpg", ios::out | ios::binary);
    if(reader.fail()) {
        cout << "Failed to open file" << endl; 
        return 1;
    }
    if(writer.fail()) {
        cout << "Failed to open write stream" << endl; 
        return 1;
    }
    
    while(!reader.eof()) {
        reader.read(&buffer,1);
        writer.write(&buffer,1);
    }
    reader.close();
    writer.close();
    
    return 0;
}

This seemed to work for me, except for the one small problem that the resulting file is one byte larger than the initial file. Maybe someone else can spot this other problem?

I see. Then is there some way to recognize when the istream encounters no more data; other than by using EOF (which I just read doesn't really work the way the name implies)?

Like this:

Code:

while(reader.read(&buffer,1))
{
  //stuff
}

Ok...so I posted my solution, and then I read Prelude's post, and I thought "I didn't know that. Let me look at the FAQ and see what this is all about." So I went to the FAQ and I used the search bar at the bottom and I searched on "eof()". I got one hit, for a very long thread about some text based game or something, and I thought, "If the answer is buried in there somewhere, then forget it." So clearly I have no idea how to search the FAQ and make good use of it. Is there a FAQ for the FAQ?

http://faq.cprogramming.com/cgi-bin/...&id=1043284351
and thank you all.

You know, the confusion I had was that whenever I hear people talking abou the FAQ, I always think of the FAQ message board. I didn't realize that there was FAQ pages on the site. And the FAQ explains why my code produces an output file that is one byte larger.

You know, the confusion I had was that whenever I hear people talking abou the FAQ, I always think of the FAQ message board. I didn't realize that there was FAQ pages on the site. And the FAQ explains why my code produces an output file that is one byte larger.

There's a simpler way to do the copying:

Code:

#include <cstdlib>
#include <iostream>
#include <fstream>
using namespace std;

int main(int argc, char *argv[])
{
    ifstream reader("C:\\windows\\desktop\\1.jpg", ios::in | ios::binary);
    ofstream writer("C:\\windows\\desktop\\1_out.jpg", ios::out | ios::binary);

    if(reader.fail())
    {cout << "Failed to open file" << endl; return 1;}
    if(writer.fail())
    {cout << "Failed to open write stream" << endl; return 1;}
    
    // Copies entire contents of reader stream into writer stream
    writer << reader.rdbuf();
    
    system("PAUSE");
    return EXIT_SUCCESS;
}