convert boost::iostream::stream to std::istream

Question

I would like to expose streams in my code as their standard equivalents to eliminate user dependency on boost::iostreams. Would like to do this efficiently of course without creating a copy if necessary. I thought about just setting the std::istream's buffer to the one being used by the boost::iostream::stream<boost::iostreams::source>, however, this could cause ownership problems. How do you convert boost::iostream to std::iostream equivalent? Particularly boost::iostream::stream<boost::iostreams::source> to std::istream.

Answer 1

No conversion is needed:

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#include <iostream>
#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/device/array.hpp>

namespace io = boost::iostreams;

void foo(std::istream& is) {
    std::string line;
    while (getline(is, line)) {
        std::cout << " * '" << line << "'\n";
    }
}

int main() {
    char buf[] = "hello world\nbye world";
    io::array_source source(buf, strlen(buf));
    io::stream<io::array_source> is(source);

    foo(is);
}

Other than that I don't think you could have ownership issues, since std::istream doesn't assume ownership when assigned a new rdbuf:

• Why doesn't std::istream assume ownership over its streambuf?

So, you're also free to do:

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std::istream wrap(is.rdbuf());
foo(wrap);

Printing the same