Get a C-style String from a String Type

extract_c_string

extract_c_string returns a pointer to an array of elements of a const character type. It is invoked through a static method call. This customization point is responsible for handling it's own garbage collecting; the lifetime of the returned C-string must be no shorter than the lifetime of the string instance passed to the call method.

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 String>
struct extract_c_string
{
    typedef <unspecified> char_type;

    static char_type const* call (String const&);
};

Template parameters

Parameter	Description	Default
`String`	A string type.	none

Notation

T: An arbitrary type.
Char: A character type.
Traits: A character traits type.
Allocator: A standard allocator type.
str: A string instance.

Expression Semantics

Expression	Semantics
`extract_c_string<T>::char_type`	The return type of `call`.
`extract_c_string<T>::call(str)`	Extract a c-string of type `char_type` from `str`.

Predefined Specializations

Type	Semantics
`T`	`call` takes a parameter of type `T const`, and returns it without modification. An overload of `call` takes a parameter of type `T` and casts it to `T const*`, returning the result. `char_type` is `char_type_of<T>::type`.
`T const`	`call` takes a parameter `str` of type `T const` and returns `extract_c_string<T>::call(str)`. `char_type` is `char_type_of<T>::type`.
`T&`	`call` takes a parameter `str` of type `T&` and returns `extract_c_string<T>::call(str)`. `char_type` is `char_type_of<T>::type`.
`T const&`	`call` takes a parameter `str` of type `T const&` and returns `extract_c_string<T>::call(str)`. `char_type` is `char_type_of<T>::type`.
`std::basic_string<Char, Traits, Allocator>`	`call` takes a parameter `str` and returns `str.c_str()`. `char_type` is `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 `extract_c_string` is implemented.
`traits::char_type_of`	Whenever `extract_c_string` is implemented.