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post Trying to override streambuf to use with cout

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Join Date: Jan 2009

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rob_l_f

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post Trying to override streambuf to use with cout

Jan 11th, 2009

Hi,

I'm trying to grab all the input sent to cout to modify and redirect it. I used the example from http://www.dreamincode.net/code/snippet2499.htm, which works fine using the following code:

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    std::ofstream file_sink("encrypted.bin", std::ios_base::binary | std::ios_base::out);
    basic_xor_filter<char> filter(*(file_sink.rdbuf()), 0x7F);
    std::ostream output_stream(&filter);
    output_stream << "Hello World" << std::endl;
    output_stream.flush();
    std::ofstream file_sink("encrypted.bin", std::ios_base::binary | std::ios_base::out);
    basic_xor_filter<char> filter(*(file_sink.rdbuf()), 0x7F);
    std::ostream output_stream(&filter);
    output_stream << "Hello World" << std::endl;
    output_stream.flush();

The class overrides streambuf and simply XORs the input characters before sending them to the provided streambuf (in this case, a file). My problem occurs when I try setting cout's rdbuf() to filter:

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    streambuf* s = &filter;
    cout.rdbuf( s );
    cout << "Hello World\n";
    streambuf* s = &filter;
    cout.rdbuf( s );
    cout << "Hello World\n";

This code causes a glibc "double free or corruption (!prev)" error. Could anyone tell me where I am going wrong? Perhaps I just don't understand the concepts properly?

Thanks very much.

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Join Date: Dec 2007

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jencas

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Re: post Trying to override streambuf to use with cout

Jan 12th, 2009

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        streambuf* s = &filter;
        streambuf* old = cout.rdbuf(s);
        cout << "Hello World" << endl;
        cout.flush();
        cout.rdbuf(old);
        streambuf* s = &filter;
        streambuf* old = cout.rdbuf(s);
        cout << "Hello World" << endl;
        cout.flush();
        cout.rdbuf(old);