FBB::OFilterStreambuf - Base class for std::ostream filtering
#include <bobcat/ofilterstreambuf>
Linking option: -lbobcat
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).
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
- 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).
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.
- o
- std::ostream &out() const:
This member is available to derived classes to insert information into the
destination (filtered) stream.
#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
}
bobcat/ofilterstreambuf - defines the class interface
- o
- bobcat_4.08.06-x.dsc: detached signature;
- o
- bobcat_4.08.06-x.tar.gz: source archive;
- o
- bobcat_4.08.06-x_i386.changes: change log;
- o
- libbobcat1_4.08.06-x_*.deb: debian package holding the
libraries;
- o
- libbobcat1-dev_4.08.06-x_*.deb: debian package holding the
libraries, headers and manual pages;
- o
- 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).