Output stream help

This is a discussion on Output stream help within the C++ Programming forums, part of the General Programming Boards category; Hi, I have implemented the virtual function of the streambuf class In specification is written that overflow() function is callled ...

  1. #1
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    Output stream help

    Hi,

    I have implemented the virtual function of the streambuf class
    In specification is written that overflow() function is callled when buffer is full.
    but i have observed that this function ( overflow() ) is called on writing the each character in output stream e.g. on writing the abc , this function is called three times Why?????
    Is the specification wrong or default buffer size is one byte?


    Code:
    cout.rdbuf(&DebugStreamBuf);
    
    cout << abc << endl;
    
    int DebugStreamBuf::overflow(int ch)
    {
     ...
    }

  2. #2
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    It does seem like you need to set the buffer & size using setbuf().

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    Mats
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    what is the default streambuf size? Would you please shortly describe the whole process.

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    Quote Originally Posted by alibaba786 View Post
    what is the default streambuf size? Would you please shortly describe the whole process.
    I have never done that - I'm just guessing from the cppreference.

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    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
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  5. #5
    Cat without Hat CornedBee's Avatar
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    matsp is right. You need to set a buffer if you don't want overflow() to be called for every character. How large the buffer is is up to you - but you have to manage it. I guess typical sizes will be about 4k.
    All the buzzt!
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    It means , if i dont set the buffer size , output stream consider the buffer size . am i right???
    Is it specified somewhere??

  7. #7
    Cat without Hat CornedBee's Avatar
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    You actually have to provide the buffer. The size just needs to match the buffer. This is documented in the C++ standard, in the description of basic_streambuf. Although, of course, in standardese.

    The best resource for using streams is "Standard C++ IOStreams and Locales", by Langer and Kreft, Addison Wesley.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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    My question still the same, if i dont set the buffer size , what would be the buffer size?
    or by default output stream sets the buffer size = 1 byte???
    Is it specified somewhere??

  9. #9
    Cat without Hat CornedBee's Avatar
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    If you don't set a buffer, there is no buffer, so the buffer size is 0. Thus, every character immediately overflows.
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    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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  10. #10
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    Thanks . now i have got the answer ...

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