FBB::Pipe(3bobcat)

System Level Communication Pipe
(libbobcat-dev_6.04.00)

2005-2023

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 object 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 might even be destroyed. The using code is responsible for closing the pipe. If the pipe should be closed at destruction time, then a class could be derived from Pipe(3bobcat), whose destructor may then close the pipe. Alternatively, Pope's close member can be called.

The value -1 indicates that a file descriptor does not refer to a pipe(2) file descriptor.

NAMESPACE

FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace FBB.

INHERITS FROM

-

CONSTRUCTORS

Copy construction and copy assignment are not defined.

Note that Pipe's destructor does not close the pipe's file descriptors. To close the pipes close must be called.

OVERLOADED OPERATOR

MEMBER FUNCTIONS

PROTECTED ENUMERATION

The RW protected enumeration has the following elements:

PROTECTED MEMBER FUNCTION

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 pipe;                         // construct a pipe

        cout << "Read file descriptor: " << pipe.readFd() << "\n"
                "Write file descriptor: " << pipe.writeFd() << endl;

        int pid = fork();

        if (pid == -1)
            return 1;

        if (pid == 0)                       //child
        {
            pipe.readFrom(STDIN_FILENO);    // read what goes into the pipe

            string s;

            getline(cin, s);
            cout << "CHILD: Got `" << s << "'\n";

            getline(cin, s);
            cout << "CHILD: Got `" << s << "'\n";

            return 0;
        }

        pipe.writtenBy(STDOUT_FILENO);      // write to the pipe via cout

        cout << "first line" << "\n"
                "second line" << '\n';

        waitpid(pid, 0, 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 a Pipe object goes out of scope, no close(2) operation is performed on the pipe's ends. If the pipe should be closed by the destructor, derive a class from Pipe(3bobcat), whose destructor performs the required closing-operation.

BOBCAT PROJECT FILES

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).