The Token Type

#  | The Token Type |

> Introduction
> Header 'wave/context.hpp' synopsis
> Template parameters
> Public Typedefs
> Member functions

## Introduction

The token type in `Wave` is the main carrier of information. It is returned by dereferencing the iterators exposed by the lexing component and the iterator exposed by the preprocessor component. The tokens are originally generated by the lexer ("An entity that lexically transforms the subject of parsing to a sequence of objects (called tokens) more suitable for subsequent parsing."). The Wave library contains two different, interchangable C++ lexers, which may be used as a starting point during developing your own application. The lexer generated tokens are transformed by the preprocessing engine (macro expansion, include file processing etc.) and after this returned to the user of the `Wave` library.

You can use arbitrary token types in conjunction with your own lexer as long as these implement some required interface. The required token type interface is described below and is implemented by the `wave::cpplexer::lex_token` template, the required lexer interface is described here.

In the following is described the token type predefined inside the `Wave` library, which is used in conjunction with the two predefined C++ lexers contained in the `Wave` library too. If you need to use your own token type, it is required to implement the interafce described below.

## Header wave/cpplexer/cpp_lex_token.hpp synopsis

    namespace boost {
    namespace wave {
    namespace cpplexer {

        template <typename Position>
        class lex_token
        {
        public:
            typedef std::basic_string<char> string_type;
            typedef Position                position_type;

            lex_token();
            lex_token(token_id id, string_type const &value,
                PositionT const &pos);

        // accessors
            operator token_id() const;
            string_type const &get_value() const;
            position_type const &get_position() const;
            void set_token_id (token_id id);
            void set_value (string_type const &newval);
            void set_position (position_type const &pos);
        };

    }   // namespace cpplexer
    }   // namespace wave
    }   // namespace boost

## Template parameters

The predefined token type uses a template parameter `Position`, which allows to specify the type to be used to carry the file position information contained inside the generated tokens. Your own token type do not need to take this `Position` template parameter, but please note, that the token type in any case needs to have an embedded type definition `position_type` (see below) .

## Public Typedefs

The token type needs to define two embedded types: `string_type` and `position_type`. The `string_type` needs to be a type compatible to the `std::basic_string<>` class.

This type should contain at least the filename, the line number and the column number of the position, where the token was recognized. For the predefined token type it defaults to a simple file_position template class described here. Note, that your own `position_type` should follow the interface described for the file_position template as well.

## Member functions

Constructors

        lex_token();

        lex_token(token_id id,
            string_t const &value,
            PositionT const &pos);

> The first (default) constructor is for generating an end of stream token, which is used for indicating the end of the underlying input stream.

> The second constructor initializes the newly created token object with its token id (for a list of valid token id's please look here), the string representation of its value and the file position, describing the position inside the input stream , where this token was recognized.

## Accessor functions

operator token_id

        operator token_id() const;

> Allows the access to the token id of the token. This accessor allows the usage of `Spirit` parsers directly on top top of a token stream generated by Wave. The possible token id's are described here.

> This function does not throw in any case.

get_value

        string_type const &get_value() const;

> Returns the value of the token, as it was recognized in the input stream. Even for constant tokens (as keywords or operators etc.) the returned value reflects the character sequence as found in the input stream.

> This function does not throw in any case.

get_position

        Position const &get_position() const;

> Returns the position of the token in the input stream, where it was recognized. The position contains information about the filename, the line number and the column number of the token. By default the `Wave` library uses a file_position template for this purpose, which is described in more detail here.

> This function does not throw in any case.

set_token_id

        void set_token_id(token_id id);

> Changes the token id of the token to the new value. The possible token id's are described here. Probably this function is of little value for the library user, but it is required under certain circumstances for correct operation of the preprocessing engine.

> This function does not throw in any case.

set_value

        void set_value(string_type const &newval);

> Changes the value stored inside the token to the new value. Propably this function is of little value for the library user, but it is required under certain circumstances for correct operation of the preprocessing engine.

set_position

        void set_position(Position const &newpos);

> Changes the position stored inside the token to the new value. This is used for instance for implementing the functionality required for to implement the `#line` directive.

Copyright © 2003-2005 Hartmut Kaiser
Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

Last updated: Thursday, December 1, 2005 21:27