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std::ranges::cdata

From cppreference.com
< cpp‎ | ranges
 
C++
 
Ranges library
Range adaptors
 
Defined in header <ranges>
Defined in header <iterator>
inline namespace /*unspecified*/ {

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

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

    requires /* see below */

constexpr /* see below */ cdata( T&& t );
 (since C++20)

Returns a pointer to the first element of constant type(since C++23) of a contiguous range denoted by a const-qualified(until C++23) 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)).

The return type is equivalent to std::remove_reference_t<ranges::range_reference_t<CT>>*.

(until C++23)

If the argument is an lvalue or ranges::enable_borrowed_range<std::remove_cv_t<T>> is true, then a call to ranges::cdata is expression-equivalent to:

The return type is equivalent to std::remove_reference_t<ranges::range_const_reference_t<T>>*.

In all other cases, a call to ranges::cdata is ill-formed, which can result in substitution failure when the call appears in the immediate context of a template instantiation.

(since C++23)

If ranges::cdata(t) is valid, then it returns a pointer to an object of constant type(since C++23).

Customization point objects

The name ranges::cdata denotes a customization point object, which is a const function object of a literal semiregular class type. See CustomizationPointObject for details.

[edit] 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!

[edit] See also

(C++20)
 obtains a pointer to the beginning of a contiguous range
(customization point object)[edit]
(C++17)
 obtains the pointer to the underlying array
(function template) [edit]
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