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.