flexc++api(3)

flexc++ API
(flexc++.2.06.02.tar.gz)

2008-2017

NAME

flexc++api - Application programmer's interface of flexc++ generated classes

DESCRIPTION

Flexc++(1) was designed after flex(1) and flex++(1). Like these latter two programs flexc++ generates code performing pattern-matching on text, possibly executing actions when certain regular expressions are recognized.

Refer to flexc++(1) for a general overview. This manual page covers the Application Programmer's Interface of classes generated by flexc++, offering the following sections:

1. INTERACTIVE SCANNERS

An interactive scanner is characterized by the fact that scanning is postponed until an end-of-line character has been received, followed by reading all information on the line, read so far. Flexc++ supports the %interactive directive), generating an interactive scanner. Here it is assumed that Scanner is the name of the scanner class generated by flexc++.

Caveat: generating interactive and non-interactive scanners should not be mixed as their class organizations fundamentally differ, and several of the Scanner class's members are only available in the non-interactive scanner. As the Scanner.h file contains the Scanner class's interface, which is normally left untouched by flexc++, flexc++ cannot adapt the Scanner class when requested to change the interactivity of an existing Scanner class. Because of this support for the --interactive option was discontinued at flexc++'s 1.01.00 release.

The interactive scanner generated by flexc++ has the following characteristics:

This implementation allows code calling Scanner::lex() to conclude, as usual, that the input is exhausted when lex returns 0.

Here is an example of how such a scanner could be used:

2. THE CLASS INTERFACE: SCANNER.H

By default, flexc++ generates a file Scanner.h containing the initial interface of the scanner class performing the lexical scan according to the specifications given in flexc++'s input file. The name of the file that is generated can easily be changed using flexc++'s --class-header option. In this man-page we'll stick to using the default name.

The file Scanner.h is generated only once, unless an explicit request is made to rewrite it (using flexc++'s --force-class-header option).

The provided interface is very light-weight, primarily offering a link to the scanner's base class (see this manpage's sections 8 through 16).

Many of the facilities offered by the scanner class are inherited from the ScannerBase base class. Additional facilities offered by the Scanner class. are covered below.

3. NAMING CONVENTION

All symbols that are required by the generated scanner class end in two consecutive underscore characters (e.g., executeAction__). These names should not be redefined. As they are part of the Scanner and ScannerBase class their scope is immediately clear and confusion with identically named identifiers elsewhere is unlikely.

Some member functions do not use the underscore convention. These are the scanner class's constructors, or names that are similar or equal to names that have historically been used (e.g., length). Also, some functions are offered offering hooks into the implementation (like preCode). The latter category of function also have names that don't end in underscores.

4. CONSTRUCTORS

5. PUBLIC MEMBER FUNCTIONS

6. PRIVATE MEMBER FUNCTIONS

7. SCANNER CLASS HEADER EXAMPLE


#ifndef Scanner_H_INCLUDED_
#define Scanner_H_INCLUDED_

// $insert baseclass_h
#include "Scannerbase.h"

// $insert classHead
class Scanner: public ScannerBase
{
    public:
        explicit Scanner(std::istream &in = std::cin,
                                std::ostream &out = std::cout);

        Scanner(std::string const &infile, std::string const &outfile);
        
        // $insert lexFunctionDecl
        int lex();

    private:
        int lex__();
        int executeAction__(size_t ruleNr);

        void print();
        void preCode();     // re-implement this function for code that must 
                            // be exec'ed before the patternmatching starts

        void postCode(PostEnum__ type);    
                            // re-implement this function for code that must 
                            // be exec'ed after the rules's actions.
};

// $insert scannerConstructors
inline Scanner::Scanner(std::istream &in, std::ostream &out)
:
    ScannerBase(in, out)
{}

inline Scanner::Scanner(std::string const &infile, std::string const &outfile)
:
    ScannerBase(infile, outfile)
{}

// $insert inlineLexFunction
inline int Scanner::lex()
{
    return lex__();
}

inline void Scanner::preCode() 
{
    // optionally replace by your own code
}

inline void Scanner::postCode(PostEnum__ type) 
{
    // optionally replace by your own code
}

inline void Scanner::print() 
{
    print__();
}

#endif // Scanner_H_INCLUDED_
        

8. THE SCANNER BASE CLASS

By default, flexc++ generates a file Scannerbase.h containing the interface of the base class of the scanner class also generated by flexc++. The name of the file that is generated can easily be changed using flexc++'s --baseclass-header option. In this man-page we use the default name.

The file Scannerbase.h is generated at each new flexc++ run. It contains no user-serviceable or extensible parts. Rewriting can be prevented by specifying flexc++'s --no-baseclass-header option).

9. PUBLIC ENUMS AND -TYPES

10. PROTECTED ENUMS AND -TYPES

11. NO PUBLIC CONSTRUCTORS

There are no public constructors. ScannerBase is a base class for the Scanner class generated by flexc++. ScannerBase only offers protected constructors.

12. PUBLIC MEMBER FUNCTIONS

13. PROTECTED CONSTRUCTORS

14. PROTECTED MEMBER FUNCTIONS

All member functions ending in two underscore characters are for internal use only and should not be called by user-defined members of the Scanner class.

The following members, however, can safely be called by members of the generated Scanner class:

15. PROTECTED DATA MEMBERS

All protected data members are for internal use only, allowing lex__ to access them. All of them end in two underscore characters.

16. FLEX++ TO FLEXC++ MEMBERS


Flex++ (old) Flexc++ (new)

lineno() lineNr()
YYText() matched()
less() accept()

17. THE CLASS INPUT

Flexc++ generates a file Scannerbase.h defining the scanner class's base class, by default named ScannerBase (which is the name used in this man-page). The base class ScannerBase contains a nested class Input whose interface looks like this:


class Input
{
    public:
        Input();
        Input(std::istream *iStream, size_t lineNr = 1);
        size_t get();
        size_t lineNr() const;          
        size_t nPending() const;          
        void setPending(size_t nPending);          
        void reRead(size_t ch);
        void reRead(std::string const &str, size_t fmIdx);
        void close();
};
        
The members of this class are all required and offer a level in between the operations of ScannerBase and flexc++'s actual input file that's being processed.

By default, flexc++ provides an implementation for all of Input's required members. Therefore, in most situations this section of this man-page can safely be ignored.

However, users may define and extend their own Input class and provide flexc++'s base class with that Input class. To do so flexc++'s rules file must contain the following two directives:


       %input-implementation = "sourcefile"
       %input-interface = "interface"
        
Here, interface is the name of a file containing the class Input's interface. This interface is then inserted into ScannerBase's interface instead of the default class Input's interface. This interface must at least offer the aforementioned members and constructors (their functions are described below). The class may contain additional members if required by the user-defined implementation. The implementation itself is expected in sourcefile. The contents of this file are inserted in the generated lex.cc file instead of Input's default implementation. The file sourcefile should probably not have a .cc extension to prevent its compilation by a program maintenance utility.

When the lexical scanner generated by flexc++ switches streams using the //include directive (see also section 2. FILE SWITCHING) in the flexc++input(7) man page), then the input stream that's currently processed is pushed on an Input stack maintained by ScannerBase, and processing continues at the file named at the //include directive. Once the latter file has been processed, the previously pushed stream is popped off the stack, and processing of the popped stream continues. This implies that Input objects must be `stack-able'. The required interface is designed to satisfy this requirement.

18. INPUT CONSTRUCTORS

19. REQUIRED PUBLIC MEMBER FUNCTIONS

FILES

Flexc++'s default skeleton files are in /usr/share/flexc++.
By default, flexc++ generates the following files:

SEE ALSO

flexc++(1), flexc++input(7)

BUGS

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),
Jean-Paul van Oosten (j.p.van.oosten@rug.nl),
Richard Berendsen (richardberendsen@xs4all.nl) (until 2010).