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- <div class="titlepage"><div><div><h2 class="title" style="clear: both">
- <a name="variadic_macro_data.vmd_data_types"></a><a class="link" href="vmd_data_types.html" title="Data types">Data types</a>
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- <p>
- The VMD library has functionality for testing and parsing preprocessor data.
- </p>
- <p>
- The C++ preprocessor defines preprocessor data as preprocessing tokens. The
- types of preprocessing tokens can be seen in section 2.5 of the C++ standard
- document.
- </p>
- <p>
- The VMD library works with a subset of two of these types of preprocessor tokens
- as "data types". These are the "identifier" and "pp-number"
- preprocessor tokens. The preprocessor token types which VMD cannot parse are:
- </p>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- header-name
- </li>
- <li class="listitem">
- character-literal
- </li>
- <li class="listitem">
- user-defined-characteral-literal
- </li>
- <li class="listitem">
- string-literal
- </li>
- <li class="listitem">
- user-defined-string-literal
- </li>
- <li class="listitem">
- preprocessing-op-or-punc
- </li>
- </ul></div>
- <p>
- Even though VMD cannot parse these preprocessor token types, it is still a
- very useful library since a large part of macro programming works with 'identifier'
- and 'pp-number' tokens.
- </p>
- <p>
- VMD identifiers are preprocessing tokens consisting of alphanumeric characters
- and the underscore ( _ ) character. This is very similar to a preprocessor
- token "identifier" with the difference being that a VMD identifier
- can start with a numeric character, allowing VMD identifiers to also be positive
- integral literals. VMD offers functionality for parsing VMD identifiers both
- as a separate element or in a sequence of preprocessing tokens.
- </p>
- <p>
- VMD numbers are Boost PP numbers, ie. preprocessing tokens of whole numbers
- between 0 and 256 inclusive. These are a small subset of preprocessor token
- "pp-number". VMD offers functionality for parsing numbers both as
- a separate element or in a sequence of preprocessing tokens. A VMD number is
- really a subset of VMD identifiers for which VMD offers specific functionality.
- The Boost PP library has it own extensive support for numbers, which VMD does
- not duplicate.
- </p>
- <p>
- VMD v-types are, like numbers, a subset of VMD identifiers consisting of identifiers
- beginning with BOOST_VMD_TYPE_ followed by a data type mnemonic. Each v-type
- can be recognized by VMD functionality and therefore passed or returned by
- macros. Like any identifier a v-type can be parsed both as a separate element
- or in a sequence of preprocessing tokens.
- </p>
- <p>
- VMD can also test for emptiness, or the absence of any preprocessing tokens
- when passed as macro input.
- </p>
- <p>
- The Boost PP library supports four individual high-level data types. These
- are arrays, lists, seqs, and tuples. When using variadic macros arrays are
- really obsolete since tuples have all the functionality of arrays with a simpler
- syntax. Nonetheless arrays are fully supported by VMD. A further data type
- supported by Boost PP is variadic data, which is a comma separated grouping
- of preprocessor elements. VMD has no special support for variadic data outside
- of what is already in Boost PP.
- </p>
- <p>
- VMD has functionality to work with the four Boost PP high-level data types.
- VMD can test the Boost PP data types and parse them in a sequence of preprocessor
- tokens.
- </p>
- <p>
- VMD can also parse sequences. A sequence consists of zero or more other top-level
- data types already mentioned represented consecutively. As such a sequence
- represents any data type which VMD can parse since it can consist of emptiness,
- a single data type, or multiple data types represented consecutively.
- </p>
- <p>
- Emptiness, the three identifier types, the four Boost PP composite data types,
- and VMD sequences are the data types which VMD understands. Other low-level
- preprocessor data types can of course be used in macro programming but VMD
- cannot parse such preprocessor data.
- </p>
- </div>
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