bionic (3) ofilterstreambuf.3bobcat.gz
NAME
FBB::OFilterStreambuf - Base class for std::ostream filtering
SYNOPSIS
#include <bobcat/ofilterstreambuf>
Linking option: -lbobcat
DESCRIPTION
The FBB::OFilterStreambuf class is a specialization of the std::streambuf class and can be used as a base
class for classes implementing ostream-filtering.
Ostream filtering is defined here as the process by which inserted characters are subject to processing
before they are passed on to another (filtered) ostream object (or they may be rejected). The filtering
may also result in inserting additional information into the filtered ostream.
Chaining of filters is also possible: the filtered ostream may itself use an OFilterStreambuf to filter
its received information before passing it on to yet another ostream.
As OFilterStreambuf inherits from std::streambuf an OFilterStreambuf object can be used to provide an
ostream object with a std::streambuf. Information inserted into such a stream travels the following
route:
o The information is converted to characters using the standard conversion facilities implemented by
std::ostream objects. E.g., when inserting the value 123 this value is converted to the characters
’1’, ’2’ and ’3’, respectively.
o Each of the characters is then offered (in turn) to the std::streambuf that is associated with the
ostream object. In particular, the std::streambuf’s overflow() member is called.
o OFstreamBuf’s default overflow() function ignores characters, but specializations can override
overflow() to process the received characters ad lib.
o A overriding overflow() function has access to the member OFstreambuf::out() which is a reference
to the std::ostream receiving the filtered information. To implement a simple copy-filter (i.e.,
all characters are accepted as-is) a class must be derived from OFilterStreambuf providing an
overriding implementation of overflow(), e.g., as follows:
int DerivedClass::overflow(int ch)
{
out().put(ch);
}
Next this std::streambuf specialization can be associated with an ostream into which information
to be `copy filtered’ can be inserted (cf. the EXAMPLE section below).
NAMESPACE
FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the
namespace FBB.
INHERITS FROM
std::streambuf
CONSTRUCTORS
o OFilterStreambuf():
This constructor creates a OFilterStreambuf object without associating it with a destination
(filtered) ostream.
o OFilterStreambuf(std::string const &fname, openmode mode = std::ios::out):
This constructor creates a OFilterStreambuf object and opens a private std::ofstream object whose
filename is provided and that should receive the filtered information.
o OFilterStreambuf(char const *fname, openmode mode = std::ios::out):
Same as the previous constructor, expecting a char const * defining the name of the private
std::ofstream object.
o OFilterStreambuf(std::ostream &out):
This constructor creates a OFilterStreambuf object and will insert any filtered information into
the provided ostream object. The class’s destructor closes the destination (filtered) stream
(cf. the description of close() below).
MEMBER FUNCTIONS
All members of std::ostreambuf are available, as FBB::OFilterStreambuf inherits from that class. In
particular, derived classes should provide their own implementation of int underflow(int ch) to implement
any non-trivial filtering.
o void close():
This member calls the streambuf::sync() member to flush any pending information to the destination
(filtered) stream and then closes the destination stream. Note that the default sync() member
performs no special actions but it can be overridden by derived classes to flush the destination
stream just prior to its closing.
o void open(std::string const &fname, openmode mode = std::ios::out):
This member closes the current destination (filtered) std::ostream object and associates the
OFilterStreambuf object with a private std::ofstream object whose filename is provided and that
should receive subsequently filtered information.
o void open(char const *fname, openmode mode = std::ios::out):
Same as the previous member, but using a char const * to specify the name of the private
std::ofstream object to receive the filtered information.
o void open(std::ostream &out):
This member closes the current destination (filtered) std::ostream object and associates the
OFilterStreambuf object with the provided ostream object.
PROTECTED MEMBER FUNCTION
o std::ostream &out() const:
This member is available to derived classes to insert information into the destination (filtered)
stream.
EXAMPLE
#include <iostream>
#include <cctype>
#include <bobcat/ofilterstreambuf>
class NoDigits: public FBB::OFilterStreambuf
{
private:
int overflow(int ch) override
{
if (not isdigit(ch))
out().put(ch);
return ch;
}
int sync() override
{
out() << flush;
return 0;
}
};
using namespace FBB;
using namespace std;
int main()
{
NoDigits nod(cout); // no digits to cout
ostream out(&nod);
out << in.rdbuf(); // rm digits from cin
return 0;
}
FILES
bobcat/ofilterstreambuf - defines the class interface
SEE ALSO
bobcat(7), ifilterstreambuf(3bobcat)
BUGS
None Reported.
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).