Read/Write Binary Files

This is a discussion on Read/Write Binary Files within the C++ Programming forums, part of the General Programming Boards category; I want to read/write a binary file (I'm making a game, text-based for now, graphics later) I'm using this code ...

  1. #1
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    Read/Write Binary Files

    I want to read/write a binary file (I'm making a game, text-based for now, graphics later) I'm using this code for reading/writing:

    Code:
    void player::save()
    {
    	cout << "Saving...";
    	ofstream save;
    	save.open("bin.dat", ios_base::binary);
    	if(!save.is_open())
    	{
    		cerr << "Error in file I/O";
    		exit(1);
    	}
    
    	save.write(reinterpret_cast<char *> (this), sizeof(this));
    	save.close();
    }
    
    void player::load()
    {
    	player b;
    	ifstream load;
    	load.open("bin.dat", ios_base::binary);
    	if(!load.is_open())
    	{
    		cerr << "Error in file I/O";
    		exit(1);
    	}
    
    	load.read(reinterpret_cast<char *> (&b), sizeof(&b));
    
    	cout << "Loaded: " << b.name;
    	load.close();
    }
    I took this code from my book (2 chapters ahead from my current chapter), but it doesn't work, no errors/warnings/runtime problems, but the program doesn't save the info. When I execute load() in my program (after save(), the file exists) it couts only "Loaded: " and not the b.name, is this a reading or writing problem and how can I solve it?
    Operating Systems:
    - Ubuntu 9.04
    - XP

    Compiler: gcc

  2. #2
    ZuK
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    I guess that Player.name is a std:string. So what you are saving with write is only the string object and not it's data.
    You should search for serialisation.
    There are many serialization libraries available.
    e.g. boost/serialization
    Kurt

  3. #3
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    >>save.write(reinterpret_cast<char *> (this), sizeof(this));

    this is a pointer, and the size of any pointer is a constant value, 4 on 32-bit compilers. add the asterisk (star) in front of this to get its size
    Code:
    save.write(reinterpret_cast<char *> (this), sizeof(*this));
    That will write the class, but if the class contains std::string or any other std:: containers that line will not write them out. Each of those objects have to be written out individually, which might take a little pre-planning on your part.

  4. #4
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    I think I'm not going to use binary storage, I'll just use the overloaded >> and << operators. Can I use the encryption algorithm of the code snippets for encryption? (Against cheaters :P)
    Operating Systems:
    - Ubuntu 9.04
    - XP

    Compiler: gcc

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    I just made my own simple encryption, I made it so any character you type is the opposite, like, if you type A, and save it. It is saved as Z, or 0 is 9, and so on. THat will work for most cheaters, but hackers it doesnt matter what you do they can crack it.

  6. #6
    Super Moderator VirtualAce's Avatar
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    Writing variable length strings to disk is a pain in the arse b/c you can't just stick the data in a structure and do a block read/write. You can either overload operators to work with string data types or you can specify the length of the string in a member and then read in that many bytes.

    MFC's CString and CArchive are extremely handy as they let you use insertion and extraction operators on all standard data types and on CStrings. A CString object knows how to read and write itself to/from disk. You may be able to use these by simply linking with the MFC DLL as a shared DLL. You do not have to have a complete MFC program to use the utilities in MFC.

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    According to the poster's sig, his OS is SUSE, and his compiler is g++. I'm guessing he is going to run into problems attempting to use MFC.

  8. #8
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    Oops, I need to change my sig.. I use Ubuntu now, and windows works again! :P
    Operating Systems:
    - Ubuntu 9.04
    - XP

    Compiler: gcc

  9. #9
    Super Moderator VirtualAce's Avatar
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    Well since I don't even know what the hell Ubuntu is, I'd say switch OS's.

  10. #10
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    Quote Originally Posted by Bubba
    Well since I don't even know what the hell Ubuntu is, I'd say switch OS's.

    google

  11. #11
    Super Moderator VirtualAce's Avatar
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    Strange name.

  12. #12
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    It's the easiest linux distro (they say: "Linux for human beings") It is very easy, and has a lot of windows things working. "Ubuntu" means something like "Being humain to other people", and "I am what I am by what we are" in old-African (Translated from Dutch ).
    Operating Systems:
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    Compiler: gcc

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