[Boost-users] stream + file_descriptor_source + closing

From: Tomasz Noiñski (noix_at_[hidden])
Date: 2007-07-30 09:56:25

Hi,

I'm trying to use boost::iostreams for a project I'm writing and I have
a problem:

It seems that the destructor of
boost::iostreams::stream<boost::iostreams::file_descriptor_source> closes
the file descriptor.
I really need to be able to close this file descriptor manually and I
can't find any way to do it.

Note that file_descriptor_source has a constructor parameter specifying if
the descriptor should be closed in file_descriptor_source destructor or
not. It perfectly works - it's boost::iostreams::stream destructor that
forces closing the description, not file_descriptor_source destructor.

A short code illustrating this problem (for Linux):

--- 8< ---

#include <iostream>
#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/iostreams/stream.hpp>
#include <cstring>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

using namespace std;
using namespace boost::iostreams;

int main() {
        int fd = open("/etc/fstab", O_RDONLY);
        clog << "fd=" << fd << endl;
        {
                file_descriptor_source source(fd, false);
                stream<file_descriptor_source> strm(source);
                string s;
                strm >> s;
                clog << "first line: " << s << endl;
        }
        int closeRet = close(fd);
        int closeErrno = errno;
        clog << "closing result: " << closeRet << ", "
                << strerror(closeErrno) << endl;
}

--- 8< ---

The behaviour I would expect is the close() at the end succeeding.
However, it returns -1 with errno=EBADF.

Is this the expected behaviour or a bug?

TIA,

Noix