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std::ranges::cdata(3) C++ Standard Libary std::ranges::cdata(3) NAME std::ranges::cdata - std::ranges::cdata Synopsis Defined in header <ranges> Defined in header <iterator> inline namespace /*unspecified*/ { inline constexpr /*unspecified*/ cdata = (since C++20) /*unspecified*/; (customiza- tion point object) } Call signature template< class T > requires /* see below */ (since C++20) constexpr /* see below */ cdata( T&& t ); 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. (until C++23) 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>>*. 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: * /*as-const-pointer*/(ranges::data(/*possibly-const-range*/(t))). (since The return type is equivalent to C++23) 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 con- text of a template instantiation. 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. 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 dif- ferent 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 inter- changeably. 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) http://cppreference.com 2024.06.10 std::ranges::cdata(3)
NAME | Synopsis | Example | Output: | See also
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