Determine the Character Type of a String

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##### Determine the Character Type of a String

###### char_type_of

This customization point is an MPL metafunction which returns the character type of a given string type. `char_type_of` handles user-defined types such as std::string, as well as C-style strings.

###### Module Headers

    #include <boost/spirit/home/support/string_traits.hpp>

Also, see Include Structure.

| Note
This header file does not need to be included directly by any user program as it is normally included by other Spirit header files relying on its content.

###### Namespace

Name
`boost::spirit::traits`

###### Synopsis

    template <typename T>
    struct char_type_of
    {
        typedef <unspecified> type;
    };

###### Template parameters

Parameter | Description | Default
--- | --- | ---
`T` | A string type. | none

Notation

`T`

  An arbitrary type.

`N`

  An arbitrary integral constant.

`Char`

  A character type.

`Traits`

  A character traits type.

`Allocator`

  A standard allocator type.

###### Expression Semantics

Expression | Semantics
--- | ---
`char_type_of<T>::type` | The character type of the string type `T`.

###### Predefined Specializations

Type | Semantics
--- | ---
`T const` | Returns `char_type_of<T>`.
`char` | Returns `char`.
`wchar_t` | Returns `wchar_t`.
`char const*` | Returns `char const`.
`wchar_t const*` | Returns `wchar_t const`.
`char*` | Returns `char`.
`wchar_t*` | Returns `wchar_t`.
`char[N]` | Returns `char`.
`wchar_t[N]` | Returns `wchar_t`.
`char const[N]` | Returns `char const`.
`wchar_t const[N]` | Returns `wchar_t const`.
`char(&)[N]` | Returns `char`.
`wchar_t(&)[N]` | Returns `wchar_t`.
`char const(&)[N]` | Returns `char const`.
`wchar_t const(&)[N]` | Returns `wchar_t const`.
`std::basic_string<Char, Traits, Allocator>` | Returns `Char`.

###### When to implement

This customization point needs to be implemented whenever `traits::is_string` is implemented.

###### Related Attribute Customization Points

If this customization point is implemented, the following other customization points need to be implemented as well.

Name | When to implement
--- | ---
`traits::is_char` | For string types whose underlying character type is not `char` or `wchar_t`, `is_char` must be implemented.
`traits::is_string` | Whenever `char_type_of` is implemented.
`traits::extract_c_string` | Whenever `char_type_of` is implemented.