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FBB::Pipe(3bobcat) System Level Communication Pipe FBB::Pipe(3bobcat)

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

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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.
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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.

Copy and move constructors (and assignment operators) are available.

MEMBER FUNCTIONS

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int readFd() const:
Returns the pipe’s file descriptor that is used for reading
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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.
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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).
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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.
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int writeFd() const:
Returns the pipe’s file descriptor that is used for writing.
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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.
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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:
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READ:
The index in d_fd[] (see below) of the element holding the pipe’s reading file descriptor;
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WRITE:
The index in d_fd[] (see below) of the element holding the pipe’s writing file descriptor

PROTECTED DATA

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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);
    }
        

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

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bobcat_5.00.03-x.dsc: detached signature;
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bobcat_5.00.03-x.tar.gz: source archive;
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bobcat_5.00.03-x_i386.changes: change log;
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libbobcat1_5.00.03-x_*.deb: debian package holding the libraries;
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libbobcat1-dev_5.00.03-x_*.deb: debian package holding the libraries, headers and manual pages;
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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).
2005-2019 libbobcat-dev_5.00.03-x.tar.gz