std::ranges::data - cppreference.com (original) (raw)

| Defined in header | | | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | ------------------------------------------ | | Defined in header | | | | inline namespace /* unspecified */ { inline constexpr /* unspecified */ data = /* unspecified */; } | | (since C++20) (customization point object) | | Call signature | | | | template< class T > requires /* see below */ constexpr std::remove_reference_t< ranges::range_reference_t<T>>* data( T&& t ); | | (since C++20) |

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 is ill-formed, no diagnostic required.

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 to:

1. decay-copy(t.data())(until C++23)auto(t.data())(since C++23), if that expression is valid and its type is a pointer to an object type.
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) appears in the immediate context of a template instantiation.

Customization point objects

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

[edit] 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 is ill-formed, which also results in substitution failure.

If ranges::data(e) is valid for an expression e, then it returns a pointer to an object.

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 to match the implementations.

[edit] Example

#include #include #include #include   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; }

Output:

[edit] See also

| | obtains a pointer to the beginning of a read-only contiguous range(customization point object)[edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | returns an iterator to the beginning of a range(customization point object)[edit] | | | obtains the pointer to the underlying array (function template) [edit] |