--- name: "ofilterstreambuf" section: "3bobcat" platform: "linux" package: "libbobcat-dev" version: "4.08.06-1" release: "Debian 10 (Buster)" platforms: ["linux"] url: "https://new.carta.tech/ofilterstreambuf" --- # ofilterstreambuf(3bobcat) Base class for std::ostream filtering ## NAME FBB::OFilterStreambuf - Base class for std::ostream filtering ## SYNOPSIS **#include \**\ 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 #include #include 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 } ``` ## FILES *bobcat/ofilterstreambuf* - defines the class interface ## SEE ALSO [**bobcat**(7)](/bobcat/7.md), [**ifilterstreambuf**(3bobcat)](/ifilterstreambuf/3bobcat.md) ## BUGS None Reported. ## DISTRIBUTION FILES - 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 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**).