std::ranges::cdata
Defined in header <ranges> |
||
---|---|---|
inline namespace /*unspecified*/ { inline constexpr /*unspecified*/ cdata = /*unspecified*/; } |
(since C++20) (customization point object) |
|
Call signature | ||
template< class T > requires /* see below */ constexpr std::remove_reference_t<ranges::range_reference_t</*CT*/>>* cdata( T&& t ); |
(since C++20) |
Returns a pointer to the first element of a contiguous range denoted by a const-qualified argument.
Let CT
be.
-
const std::remove_reference_t<T>&
if the argument is an lvalue (i.e.T
is an lvalue reference type), -
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
andf
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
#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
(C++20)
|
obtains a pointer to the beginning of a contiguous range (customization point object) |
(C++17)
|
obtains the pointer to the underlying array (function template) |
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