ext/stdio_filebuf

[Daniel Franke <franke dot daniel at gmail dot com>]

Hi all.

I wanted to employ C++ streams on posix file descriptors obtained by pipe(). 
The extension class stdio_filebuf serves exactly this purpose. 

There are two non-default constructors for stdio_filebuf, one takes a posix 
file descriptior, the other one a pointer to FILE. The docs [1] for the first 
constructor state:
  "This constructor associates a file stream buffer with an open POSIX file
   descriptor. The file descriptor will be automatically closed when the
   stdio_filebuf is closed/destroyed."

For the second:
  "This constructor associates a file stream buffer with an open C FILE*.
   The FILE* will not be automatically closed when the stdio_filebuf is
   closed/destroyed."

Why was the closing behaviour upon destruction implemented differently?

Assume a function as
  void transform(int infd, int outfd) {
    stdio_filebuf<char> inbuf(infd, std::ios::in); 
    std::istream in(&inbuf);

    stdio_filebuf<char> outbuf(outfd, std::ios::out); 
    std::ostream out(&outbuf);

    // read from in, write to out
  }

where in infd/outfd may either be pipes, files, STD*_FILENO constants or  
anything else that is suitable. Using stdio_filebuf on infd=STDIN_FILENO or 
outfd=STDOUT_FILENO will close stdin/stdout of the current process as soon as 
the in and out streams are destroyed -- one would like to avoid that.

A blog [2] indicates that there are buffering problems of some kind if the 
constructor for POSIX file descriptors is used and proposes a workaround 
using the FILE* based constructor. Are these problems known?

For now, I'm resorting to posix read/write functions instead of stdio_filebuf.


Regards
	Daniel 


[1] 
http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/class____gnu__cxx_1_1stdio__filebuf.html
[2] http://synflood.at/blog/index.php?/plugin/tag/c%2B%2B