Provided by: libbobcat-dev_4.08.02-2build1_amd64 
NAME
FBB::Pipe - Defines a system level communication pipe
SYNOPSIS
#include <bobcat/pipe>
Linking option: -lbobcat
DESCRIPTION
FBB::Pipe objects may be used to construct a pipe. Pipe objects offer a simple interface
to the reading and writing ends of pipes. Pipe objects are object-wrappers around the
pipe(2) system call.
A Pipe which is created just before a program forks can be used to set up a line of
communication between the parent and child process. Information which is written by the
child process to its standard output stream can be redirected to the writing end of the
pipe (using the writtenBy member). The information appearing at the reading end of the
pipe can then be extracted using, e.g., an IFdStream object, initialized with the Pipe’s
reading file descriptor, or the reading end of the pipe can be redirected to an existing
stream whose file descriptor is known, like cin (which uses the STDIN_FILENO file
descriptor).
When a Pipe object goes out of scope, no close(2) operation is performed on the pipe’s
file descriptors. After setting up the pipe using the Pipe’s member functions and passing
the Pipe’s file descriptors to code that uses the Pipe’s descriptors, the Pipe object
could in fact safely be destroyed. If the pipe should be closed at destruction time, a
class could be derived from Pipe(3bobcat), whose destructor performs the required
closing-operation.
NAMESPACE
FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are
defined in the namespace FBB.
INHERITS FROM
-
CONSTRUCTORS
o Pipe():
The default Pipe constructor constructs a basic pipe, calling pipe(2).
This constructor throws an Exception exception if the default Pipe constructor did
not properly complete. The thrown Exception object’s which() member shows the
system’s errno value set by the failing pipe(2) function.
o Pipe(int const *fd):
This constructor expects two file descriptors, which already define a pipe, stored
at fd. Following the construction of the Pipe object the array pointed at by fd is
no longer used by the Pipe object. The copy constructor is available.
MEMBER FUNCTIONS
o int readFd() const:
Returns the pipe’s file descriptor that is used for reading
o void readFrom(int filedescriptor):
Sets up redirection from the internal read filedescriptor to the given
filedescriptor: information written to the write-end of the pipe may be retrieved
by extracting the information from the stream that is associated with the indicated
file descriptor. E.g., after the call readFrom(STDIN_FILENO) information inserted
into the write-end of the pipe can be retrieved from cin.
o void readFrom(int const *filedescriptors, size_t n):
Sets up redirection from the internal read filedescriptor to the given
filedescriptors: information is read from the Pipe object when reading from any of
the n provided filedescriptors (experimental).
o int readOnly():
Closes the writing end of the pipe, returns the reading end’s file descriptor. This
member can be used, e.g., to construct an IFdStream object to extract the
information that is inserted into the write-end of the pipe.
o int writeFd() const:
Returns the pipe’s file descriptor that is used for writing.
o void writtenBy(int filedescriptor):
Sets up redirection from the internal write filedescriptor to the given
filedescriptor: information is written to the Pipe object when writing to the
provided filedescriptor. E.g., after the call writtenBy(STDOUT_FILENO) information
sent to the standard output stream (by either cout or by a child process (cf.
exec(3))) is inserted into the write-end of the pipe.
o void writtenBy(int const *filedescriptors, size_t n):
Sets up redirection from the internal write filedescriptor to the given
filedescriptors: information is inserted into the write-end of the Pipe object when
writing to each of the n provided filedescriptors. E.g., when passing an array of
two int values, respectively equal to STDOUT_FILENO and STDERR_FILENO to this
member, all information which is thereafter sent to the standard output or error
streams is inserted into the write-end of the pipe.
o int writeOnly():
Closes the reading end of the pipe, returns the writing end’s file descriptor.
PROTECTED ENUMERATION
The RW protected enumeration has the following elements:
o READ:
The index in d_fd[] (see below) of the element holding the pipe’s reading file
descriptor;
o WRITE:
The index in d_fd[] (see below) of the element holding the pipe’s writing file
descriptor
PROTECTED DATA
o int d_fd[2]:
The array holding the pipe’s file descriptors. The READ element contains the pipe’s
reading file descriptor, the WRITE element contains the pipe’s writing file
descriptor,
EXAMPLE
#include <bobcat/pipe>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <iostream>
#include <string>
using namespace std;
using namespace FBB;
int main()
{
Pipe p; // construct a pipe
cout << "Read file descriptor: " << p.getReadFd() << endl;
cout << "Write file descriptor: " << p.getWriteFd() << endl;
int pid = fork();
if (pid == -1)
return 1;
if (!pid) //child
{
p.readFrom(STDIN_FILENO); // read what goes into the pipe
string s;
getline(cin, s);
cout << "CHILD: Got `" << s << "’" << endl;
getline(cin, s);
cout << "CHILD: Got `" << s << "’" << endl;
return 0;
}
p.writtenBy(STDOUT_FILENO); // write to the pipe via cout
cout << "first line" << endl;
cout << "second line" << endl;
waitpid(pid, 0, 0);
return 0;
}
See also the 2nd example at fork(3bobcat)
FILES
bobcat/pipe - defines the class interface
SEE ALSO
bobcat(7), fork(3bobcat), pipe(2), mkfifo(3)
BUGS
Note that when the pipe goes out of scope, no close(2) operation is performed on the
pipe’s ends. If the pipe should be closed by the desctructor, derive a class from
Pipe(3bobcat), whose destructor performs the required closing-operation.
DISTRIBUTION FILES
o bobcat_4.08.02-x.dsc: detached signature;
o bobcat_4.08.02-x.tar.gz: source archive;
o bobcat_4.08.02-x_i386.changes: change log;
o libbobcat1_4.08.02-x_*.deb: debian package holding the libraries;
o libbobcat1-dev_4.08.02-x_*.deb: debian package holding the libraries, headers and
manual pages;
o http://sourceforge.net/projects/bobcat: public archive location;
BOBCAT
Bobcat is an acronym of `Brokken’s Own Base Classes And Templates’.
COPYRIGHT
This is free software, distributed under the terms of the GNU General Public License
(GPL).
AUTHOR
Frank B. Brokken (f.b.brokken@rug.nl).