std::ranges::data

Returns a pointer to the first element of a contiguous range.

If T is an array type and std::remove_all_extents_t < std::remove_reference_t <T>> is incomplete, then the call to ranges::data

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

1. decay-copy (t.data()) (until C++23) auto(t.data()) (since C++23)
2. Otherwise, std::to_address ( ranges::begin (t) ) , if the expression ranges::begin(t) is valid and its type models std::contiguous_iterator

In all other cases, a call to ranges::data is ill-formed, which can result in substitution failure when ranges::data(e)

Customization point objects

The name ranges::data 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 __data_fn

All instances of __data_fn are equal. The effects of invoking different instances of type __data_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::data

Given a set of types Args..., if std::declval <Args> ( ) meet the requirements for arguments to ranges::data above, __data_fn models

• std::invocable<__data_fn, Args...>
• std::invocable < const __data_fn, Args...>
• std::invocable <__data_fn&, Args...>
• std::invocable < const __data_fn&, Args...> .
  

Otherwise, no function call operator of __data_fn participates in overload resolution.

Notes

If the argument is an rvalue (i.e. T is an object type) and ranges::enable_borrowed_range < std::remove_cv_t <T>> is false, the call to ranges::data

If ranges::data(e) is valid for an expression e

The C++20 standard requires that if the underlying data function call returns a prvalue, the return value is move-constructed from the materialized temporary object. All implementations directly return the prvalue instead. The requirement is corrected by the post-C++20 proposal P0849R8

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::data(s));
    // [data(s), data(s) + size(s)] is guaranteed to be an NTBS
 
    std::cout << a;
}

Hello world!

See also