Binary file I/O

This is a discussion on Binary file I/O within the C++ Programming forums, part of the General Programming Boards category; Why doesn't this program make a carbon copy? The output file is smaller than its counterpart and does not function. ...

  1. #1
    Kiss the monkey. CodeMonkey's Avatar
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    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;
    }
    "If you tell the truth, you don't have to remember anything"
    -Mark Twain

  2. #2
    Code Goddess Prelude's Avatar
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    >while(!reader.eof())
    That's one of your problems. The FAQ will explain why.
    My best code is written with the delete key.

  3. #3
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    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?
    The crows maintain that a single crow could destroy the heavens. Doubtless this is so. But it proves nothing against the heavens, for the heavens signify simply: the impossibility of crows.

  4. #4
    Kiss the monkey. CodeMonkey's Avatar
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    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)?
    "If you tell the truth, you don't have to remember anything"
    -Mark Twain

  5. #5
    Sweet
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    Like this:
    Code:
    while(reader.read(&buffer,1))
    {
      //stuff
    }
    Woop?

  6. #6
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    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?
    The crows maintain that a single crow could destroy the heavens. Doubtless this is so. But it proves nothing against the heavens, for the heavens signify simply: the impossibility of crows.

  7. #7
    Kiss the monkey. CodeMonkey's Avatar
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    "If you tell the truth, you don't have to remember anything"
    -Mark Twain

  8. #8
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    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.
    The crows maintain that a single crow could destroy the heavens. Doubtless this is so. But it proves nothing against the heavens, for the heavens signify simply: the impossibility of crows.

  9. #9
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    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.
    The crows maintain that a single crow could destroy the heavens. Doubtless this is so. But it proves nothing against the heavens, for the heavens signify simply: the impossibility of crows.

  10. #10
    Registered User hk_mp5kpdw's Avatar
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    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;
    }
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  11. #11
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    Question writer << reader.rdbuf(); What next?

    Quote Originally Posted by hk_mp5kpdw
    Code:
    [/
    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();
    Thanks for this - this has helped me out!

    I am trying to create my own "file format". My application can save two bitmaps into one file, with some "ini" settings at the top of the file e.g.:

    [BEGININI]
    COLOR=RED;
    TEXT='SaveMyText'
    [ENDINI]
    [FILE1]
    BMP BINARY CONTENTS HERE
    [ENDFILE1]
    BMP BINARY CONTENTS HERE
    [FILE2]
    [ENDFILE2]

    I used your code above to create this file but do you know how I could parse the images back and display them?

    Any help would be appreciated - thanks!

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