Binary data -> istream

This is a discussion on Binary data -> istream within the C++ Programming forums, part of the General Programming Boards category; Assume I have a chunk of binary data in memory, I would like to turn it into an istream. How ...

  1. #1
    Confused Magos's Avatar
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    Binary data -> istream

    Assume I have a chunk of binary data in memory, I would like to turn it into an istream. How is this done? I've been thinking of using an std::stringstream first, but since the data is binary it's a bit risky I guess.

    Something along these lines:
    Code:
    void fun(char* data, int dataSize)
    {
       std::istream s(data, dataSize);
    
       stuff = s.get();
       s.read(&junk, sizeof(junk));
    }
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    Registered User Sake's Avatar
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    Why do you need to convert the bytes into a stream? It's far simpler just to work with them directly, or write your own wrapper to make sure the buffer is worked with safely. If you really do need a stream, my first attempt would be to derive from basic_streambuf and then pass a pointer to an object of that derived class to istream's constructor.

    At the moment that's the only safe and portable way I can think of.

  3. #3
    Cat without Hat CornedBee's Avatar
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    Well, the iostreams were never really intended for binary I/O. (On the other hand, we're not given an alternative...)

    Anyway, it's true that it's a little risky to use stringstreams. I don't know very much about this. I know that the C++ standard dictates that the strings works correctly even with embedded NUL characters. However, I do not know the requirements on char_traits when faced with weird characters. Neither do I know the requirements on basic_stringbuf.

    I agree with Sake. Writing your own streambuffer is probably the best choice. And make sure you post your code - something like that could be very useful. I know of at least one other person who requires what you do.
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  4. #4
    Confused Magos's Avatar
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    The reason I need this is I have a generic loader function that uses an istream, then depending on where I want to load from (a file on the HD, a file located in memory) I pass different streams to it.

    I thought of writing something of my own too, but thought if there already exists a way it would be better...
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  5. #5
    Confused Magos's Avatar
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    Are the STL header files intentionally made totally unreadable, or are the creators just bad coders???
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  6. #6
    Registered User Sake's Avatar
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    >>Are the STL header files intentionally made totally unreadable, or are the creators just bad coders???
    Templates were designed poorly. The result is a nearly impossible mass of dependencies to unravel.

  7. #7
    Carnivore ('-'v) Hunter2's Avatar
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    Perhaps you could try a basic_istringstream<unsigned char>? According to the docs provided with MSVC Beta 2005, istringstream is just a typedef for basic_istringstream<char>. On the other hand, I'm not sure how char_traits<unsigned char> works..

    Code:
    template <
    classElem,
    classTr= char_traits<Elem>,
    classAlloc= allocator<Elem>
    >
    class basic_istringstream : public basic_istream<Elem,Tr>
    It'd be nice if you can find a way to fiddle around with that so that it behaves as you want. Unfortunately, I have no idea how any of the char_traits or allocator stuff works, so I can't be of any help there.

    **EDIT**
    [useless thought of the day]
    Or you could write the data to a file and open it with a binary ifstream
    [/useless thought of the day]
    Last edited by Hunter2; 01-23-2005 at 05:21 PM.
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  8. #8
    Registered User Sake's Avatar
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    >>On the other hand, I'm not sure how char_traits<unsigned char> works..
    It doesn't. You would have to write it first because char_traits isn't specialized for unsigned char[*].

    >>Or you could write the data to a file and open it with a binary ifstream
    This is an option, though it would slow things down a bit because of the device I/O.

    [*] Unless the default char is unsigned for the implementation, but that's a dangerous assumption for this particular problem.

  9. #9
    Cat without Hat CornedBee's Avatar
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    I think MS's STL headers are intentionally unreadable.
    All the buzzt!
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