Empty file when using boost::filtering_streambuf with newline_filter

Question

I wish to write a piece of data to the file opened via std::fopen using boost::iostreams::filtering_streambuf with newline_filter.

Here is a small reproducible test case that I have been trying to work with.

It just produces an empty file.

#include <string>
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <errno.h>

#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/filter/newline.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <iosfwd>
#include <string>
#include <boost/iostreams/flush.hpp>
#include <boost/iostreams/operations.hpp>
#include <fstream>
#include <cstdio>

int main()
{
    FILE *fp = nullptr;  

    std::string d ("file");

    fp = std::fopen(d.c_str(), "w");
    const int fd = fileno(fp);

    boost::iostreams::file_descriptor_sink output(fd, boost::iostreams::never_close_handle);
    boost::iostreams::filtering_streambuf<boost::iostreams::output>obuf;

#if defined(_WIN32)
    obuf.push(boost::iostreams::newline_filter(boost::iostreams::newline::dos));
#else
    obuf.push(boost::iostreams::newline_filter(boost::iostreams::newline::mac));
#endif

    obuf.push(output);

    std::ostream buffer(&obuf);

    std::string myteststr = "Hello \n World\n";
    buffer << myteststr;

    buffer.flush();
    boost::iostreams::flush(obuf);

    return 0;
}

Is there something obvious that I am missing here ?

Answer 1

I can't reproduce that behaviour:

Live On Coliru¹

This for the compilation and execution with

g++ -std=c++14 -O2 -Wall -pedantic -pthread main.cpp -lboost_{system,iostreams} && ./a.out
file output.txt
xxd output.txt

Prints

output.txt: ASCII text, with CRLF line terminators
00000000: 4865 6c6c 6f20 0d0a 2057 6f72 6c64 0d0a  Hello .. World..

I do suggest to add the explicit fd close, although that should not technically matter.

Also, is there any reason to use FILE* in 2019? I'm assuming you're including that because of legacy code that uses it only.

---

¹ Listing:

#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/iostreams/filter/newline.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/flush.hpp>
#include <cstdio>
#include <iostream>
#include <string>

int main() {
    FILE* fp = std::fopen("output.txt", "w");
    const int fd = fileno(fp);

    boost::iostreams::file_descriptor_sink output(fd, boost::iostreams::never_close_handle);
    boost::iostreams::filtering_streambuf<boost::iostreams::output> obuf;

    obuf.push(boost::iostreams::newline_filter(boost::iostreams::newline::dos));
    obuf.push(output);

    std::ostream buffer(&obuf);

    std::string myteststr = "Hello \n World\n";
    buffer << myteststr;

    buffer.flush();
    boost::iostreams::flush(obuf);

    ::close(fd);
}