Inherited basic_fstream operator weirdness

poc_stream_weirdness.cc

#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <fstream>
#include <iostream>
#include <memory>
#include <string>

template <typename CharT>
class my_basic_fstream : public std::basic_fstream<CharT> {
public:
    my_basic_fstream(std::FILE *f) : std::basic_fstream<char>(f) {}
};

using my_fstream = my_basic_fstream<char>;

template <typename CharT>
struct get_file_stream_ {
    static inline my_basic_fstream<CharT>& call(std::FILE* f) {
        static std::unique_ptr<my_basic_fstream<CharT>> stream;
        if (!stream)
            stream.reset(new my_basic_fstream<CharT>(f));
        return *stream;
    }

};

static inline my_fstream& get_tmp_stream() {
    return get_file_stream_<char>::call(std::tmpfile());
}

int main(void) {
    my_fstream& f = get_tmp_stream();

    f << "Foo";
    f.seekg(0);

    std::string written;
    f >> written;
    f.close();

    if (written == "Foo")
        std::cout << "All is well." << std::endl;
    else
        std::cout << "Expected \"Foo\", got \"" << written << "\"." << std::endl;

    return 0;
}

poc_stream_weirdness_g++_compat.cc

#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <fstream>
#include <iostream>
#include <memory>
#include <string>

#ifdef __GNUC__
# if defined(__MINGW32__) || defined(__MINGW64__)
#  define off_t _off_t
#  define off64_t _off64_t
# endif
# include <ext/stdio_sync_filebuf.h>
# if defined(__MINGW32__) || defined(__MINGW64__)
#  undef off_t
#  undef off64_t
# endif
#endif

template <typename CharT>
class my_basic_fstream : public std::basic_fstream<CharT> {
public:
    my_basic_fstream(std::FILE* f)
#ifdef __GNUC__
            : std::basic_fstream<CharT>()
            , fbuf(new ::__gnu_cxx::stdio_sync_filebuf<CharT>(f))
#else
            : std::basic_fstream<CharT>(f)
#endif
            , file(f)
        {
#ifdef __GNUC__
            std::ios::rdbuf(&*fbuf);
#endif
        }

        my_basic_fstream(const my_basic_fstream& other) = delete;
        my_basic_fstream& operator=(const my_basic_fstream& other) = delete;

        my_basic_fstream(my_basic_fstream&& other) :
#ifdef __GNUC__
            fbuf(std::move(other.fbuf)),
#endif
            file(std::move(other.file))
        {}

        my_basic_fstream& operator=(my_basic_fstream&& other) {
#ifdef __GNUC__
            fbuf = std::move(other.fbuf);
#endif
            file = std::move(other.file);
        }

        void close(void) {
            std::basic_fstream<CharT>::flush();
            std::basic_fstream<CharT>::close();
            std::fclose(file);
        }

    private:
#ifdef __GNUC__
        std::shared_ptr<::__gnu_cxx::stdio_sync_filebuf<CharT>> fbuf;
#endif
        std::FILE* file;
};

using my_fstream = my_basic_fstream<char>;

template <typename CharT>
struct get_file_stream_ {
    static inline my_basic_fstream<CharT>& call(std::FILE* f) {
        static std::unique_ptr<my_basic_fstream<CharT>> stream;
        if (!stream)
            stream.reset(new my_basic_fstream<CharT>(f));
        return *stream;
    }
};

static inline my_fstream& get_tmp_stream() {
    return get_file_stream_<char>::call(std::tmpfile());
}

int main(void) {
    my_fstream& f = get_tmp_stream();

    f << "Foo";
    f.seekg(0);

    std::string written;
    f >> written;
    f.close();

    if (written == "Foo")
        std::cout << "All is well." << std::endl;
    else
        std::cout << "Expected \"Foo\", got \"" << written << "\"." << std::endl;

    return 0;
}