Table of Contents
Extensions allowing filebufs to be constructed from
"C" types like FILE*s and file descriptors.
The v2 library included non-standard extensions to construct
std::filebufs from C stdio types such as
FILE*s and POSIX file descriptors.
Today the recommended way to use stdio types with libstdc++
IOStreams is via the stdio_filebuf class (see below),
but earlier releases provided slightly different mechanisms.
3.0.x filebufs have another ctor with this signature:
basic_filebuf(__c_file_type*, ios_base::openmode, int_type);
This comes in very handy in a number of places, such as
attaching Unix sockets, pipes, and anything else which uses file
descriptors, into the IOStream buffering classes. The three
arguments are as follows:
__c_file_type* F
// the __c_file_type typedef usually boils down to stdio's FILE
ios_base::openmode M
// same as all the other uses of openmode
int_type B
// buffer size, defaults to BUFSIZ if not specified
For those wanting to use file descriptors instead of FILE*'s, I
invite you to contemplate the mysteries of C's fdopen().
In library snapshot 3.0.95 and later, filebufs bring
back an old extension: the fd() member function. The
integer returned from this function can be used for whatever file
descriptors can be used for on your platform. Naturally, the
library cannot track what you do on your own with a file descriptor,
so if you perform any I/O directly, don't expect the library to be
aware of it.
Beginning with 3.1, the extra filebuf constructor and
the fd() function were removed from the standard
filebuf. Instead, <ext/stdio_filebuf.h> contains
a derived class called
__gnu_cxx::stdio_filebuf.
This class can be constructed from a C FILE* or a file
descriptor, and provides the fd() function.
If you want to access a filebuf's file descriptor to
implement file locking (e.g. using the fcntl() system
call) then you might be interested in Henry Suter's RWLock class.