std::ranges::cdata(3) | C++ Standard Libary | std::ranges::cdata(3) |
NAME¶
std::ranges::cdata - std::ranges::cdata
Synopsis¶
Defined in header <ranges>
inline namespace /*unspecified*/ {
(since C++20)
inline constexpr /*unspecified*/ cdata = /*unspecified*/; (customization
point object)
}
Call signature
template< class T >
requires /* see below */
(since C++20)
constexpr
std::remove_reference_t<ranges::range_reference_t</*CT*/>>*
cdata(
T&& t );
Returns a pointer to the first element of a contiguous range denoted by a
const-qualified argument.
Let CT be
1. const std::remove_reference_t<T>& if the argument is an lvalue
(i.e. T is an
lvalue reference type),
2. const T otherwise,
a call to ranges::cdata is expression-equivalent to
ranges::data(static_cast<CT&&>(t)).
If ranges::cdata(t) is valid, then it returns a pointer to a object.
Expression-equivalent
Expression e is expression-equivalent to expression f, if
* e and f have the same effects, and
* either both are constant subexpressions or else neither is a constant
subexpression, and
* either both are potentially-throwing or else neither is
potentially-throwing
(i.e. noexcept(e) == noexcept(f)).
Customization point objects
The name ranges::cdata denotes a customization point object, which is a const
function object of a literal semiregular class type. For exposition purposes,
the
cv-unqualified version of its type is denoted as __cdata_fn.
All instances of __cdata_fn are equal. The effects of invoking different
instances
of type __cdata_fn on the same arguments are equivalent, regardless of
whether the
expression denoting the instance is an lvalue or rvalue, and is
const-qualified or
not (however, a volatile-qualified instance is not required to be invocable).
Thus,
ranges::cdata can be copied freely and its copies can be used
interchangeably.
Given a set of types Args..., if std::declval<Args>()... meet the
requirements for
arguments to ranges::cdata above, __cdata_fn models
* std::invocable<__cdata_fn, Args...>,
* std::invocable<const __cdata_fn, Args...>,
* std::invocable<__cdata_fn&, Args...>, and
* std::invocable<const __cdata_fn&, Args...>.
Otherwise, no function call operator of __cdata_fn participates in overload
resolution.
Example¶
// Run this code
#include <cstring>
#include <iostream>
#include <ranges>
#include <string>
int main()
{
std::string src {"hello world!\n"};
// std::ranges::cdata(src)[0] = 'H'; // error, src.data() is treated as
read-only
std::ranges::data(src)[0] = 'H'; // OK, src.data() is a non-const storage
char dst[20]; // storage for a C-style string
std::strcpy(dst, std::ranges::cdata(src));
// [data(src), data(src) + size(src)] is guaranteed to be an NTBS
std::cout << dst;
}
Output:¶
Hello world!
See also¶
ranges::data obtains a pointer to the beginning of a contiguous
range
(C++20) (customization point object)
data obtains the pointer to the underlying array
(C++17) (function template)
2022.07.31 | http://cppreference.com |