< cpp‎ | ranges
Defined in header <ranges>
inline namespace /*unspecified*/ {

    inline constexpr /*unspecified*/ cdata = /*unspecified*/;

(1) (since C++20)
(customization point object)
Call signature
template< class T >

    requires /* see below */

constexpr std::remove_reference_t<ranges::range_reference_t<const T>>* cdata(T&& t);

Let t be an object of type T.

ranges::cdata is expression-equivalent to:

1) ranges::data(static_cast<const T&>(std::forward<T>(t))) if t is an lvalue.
2) ranges::data(static_cast<const T&&>(std::forward<T>(t))) if t is an rvalue.

If ranges::cdata(t) is valid, then it returns a pointer to a constant object.


[edit] Expression-equivalent

Expression e is expression-equivalent to expression f, if e and f have the same effects, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

[edit] Customization point objects

The name ranges::cdata denotes a customization point object, which is a const function object of a literal semiregular class type (denoted, for exposition purposes, as cdata_ftor). All instances of cdata_ftor are equal. 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_ftor will satisfy std::invocable<const cdata_ftor&, Args...>. Otherwise, no function call operator of cdata_ftor participates in overload resolution.

[edit] Example

#include <cstring>
#include <iostream>
#include <ranges>
#include <string>
int main()
    std::string s {"Hello world!\n"};
    char a[20]; //storage for a C-style string
    std::strcpy(a, std::ranges::cdata(s));
    //[, + s.size()] is guaranteed to be an NTBS since C++11
    std::cout << a;


Hello world!

[edit] See also

obtains a pointer to the beginning of a contiguous range
(customization point object) [edit]
obtains the pointer to the underlying array
(function template) [edit]