FBB::Pipe - Defines a system level communication pipe
#include <bobcat/pipe>
Linking option: -lbobcat
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.
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
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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. The copy constructor is available.
- 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.
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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.
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
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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,
#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)
bobcat/pipe - defines the class interface
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.
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- bobcat_4.08.06-x.dsc: detached signature;
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- bobcat_4.08.06-x.tar.gz: source archive;
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- bobcat_4.08.06-x_i386.changes: change log;
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- libbobcat1_4.08.06-x_*.deb: debian package holding the
libraries;
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- libbobcat1-dev_4.08.06-x_*.deb: debian package holding the
libraries, headers and manual pages;
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- http://sourceforge.net/projects/bobcat: public archive location;
Bobcat is an acronym of `Brokken’s Own Base Classes And
Templates’.
This is free software, distributed under the terms of the GNU
General Public License (GPL).
Frank B. Brokken (f.b.brokken@rug.nl).