Provided by: libbobcat-dev_4.01.03-2ubuntu1_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 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 void verify() const:
Obsoleted, can safely be removed from source files.
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_4.01.03-x.dsc: detached signature;
o bobcat_4.01.03-x.tar.gz: source archive;
o bobcat_4.01.03-x_i386.changes: change log;
o libbobcat1_4.01.03-x_*.deb: debian package holding the libraries;
o libbobcat1-dev_4.01.03-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).