Re: Accessing the UNIX file descriptor inside an fstream

[Chris Rankin <rankincj at yahoo dot com>]

I have modified your example program to represent more
accurately what I was trying to do. This version
core-dumps, of course, due to destructor issues. Looks
like "catch 22" to me, because if I could create the
filebuf within the initialiser list then I wouldn't
need it in the first place.

Cheers,
Chris

-----------------------------------------------
#include <iostream>
#include <fstream>
#include <string>
#include <cstdio>

#include <cstring>
#include <cerrno>
#include <fcntl.h>

using namespace std;


class Bar
{
private:
  ofstream  m_file;

public:
  Bar();

  void write(const string &msg);
};


Bar::Bar()
{
    int fd = ::open("fooey.dat",
                    O_CREAT | O_WRONLY | O_APPEND,
                    S_IRUSR | S_IWUSR | S_IRGRP |
S_IROTH);
    if (fd == -1)
    {
        cerr << "Error creating descriptor: "
             << strerror(errno)
             << endl;
    }
    else if ( fcntl(fd, F_SETFD, FD_CLOEXEC) == -1 ) 
    {
        cerr << "Error setting descriptor flag: "
             << strerror(errno)
             << endl;
    }
    else
    {
        FILE *newFile = fdopen(fd, "a");

        if (!newFile)
        {
          cerr << "Error creating new stream: "
               << strerror(errno)
               << endl;
        }
        else
        {
            filebuf buf(newFile, ios_base::out |
ios_base::app);
            m_file.basic_ios<char>::rdbuf(&buf);

            write("This should appear...");
        }
    }
}


void
Bar::write(const string &msg)
{
  m_file << msg << endl;
}


int
main()
{
    Bar bar;
    bar.write("This should core-dump!");
    return 0;
}



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