| Classes | ||||
basic_string_view (C++17) | ||||
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Defined in header <string_view> | ||
template< class CharT, | (since C++17) | |
The class templatebasic_string_view describes an object that can refer to a constant contiguous sequence ofCharT with the first element of the sequence at position zero.
For abasic_string_viewstr, pointers, iterators, and references to elements ofstr are invalidated when an operation invalidates a pointer in the range[str.data(), str.data()+ str.size()).
Every specialization of | (since C++23) |
Several typedefs for common character types are provided:
Defined in header <string_view> | |
| Type | Definition |
| std::string_view(C++17) | std::basic_string_view<char> |
| std::wstring_view(C++17) | std::basic_string_view<wchar_t> |
| std::u8string_view(C++20) | std::basic_string_view<char8_t> |
| std::u16string_view(C++17) | std::basic_string_view<char16_t> |
| std::u32string_view(C++17) | std::basic_string_view<char32_t> |
Contents |
| CharT | - | character type |
| Traits | - | CharTraits class specifying the operations on the character type. Like forstd::basic_string,Traits::char_type must name the same type asCharT or the program is ill-formed. |
| Type | Definition | ||||
traits_type | Traits | ||||
value_type | CharT | ||||
pointer | CharT* | ||||
const_pointer | const CharT* | ||||
reference | CharT& | ||||
const_reference | const CharT& | ||||
const_iterator | implementation-defined constantLegacyRandomAccessIterator,
whose | ||||
iterator | const_iterator | ||||
const_reverse_iterator | std::reverse_iterator<const_iterator> | ||||
reverse_iterator | const_reverse_iterator | ||||
size_type | std::size_t | ||||
difference_type | std::ptrdiff_t |
Note:iterator andconst_iterator are the same type because string views are views into constant character sequences.
All requirements on the iterator types of aContainer applies to theiterator andconst_iterator types ofbasic_string_view as well.
| Member | Description |
const_pointerdata_ | a pointer to the underlying sequence (exposition-only member object*) |
size_typesize_ | the number of characters (exposition-only member object*) |
Constructors and assignment | |
constructs abasic_string_view(public member function)[edit] | |
| assigns a view (public member function)[edit] | |
Iterators | |
| returns an iterator to the beginning (public member function)[edit] | |
| returns an iterator to the end (public member function)[edit] | |
| returns a reverse iterator to the beginning (public member function)[edit] | |
| returns a reverse iterator to the end (public member function)[edit] | |
Element access | |
| accesses the specified character (public member function)[edit] | |
| accesses the specified character with bounds checking (public member function)[edit] | |
| accesses the first character (public member function)[edit] | |
| accesses the last character (public member function)[edit] | |
| returns a pointer to the first character of a view (public member function)[edit] | |
Capacity | |
| returns the number of characters (public member function)[edit] | |
| returns the maximum number of characters (public member function)[edit] | |
| checks whether the view is empty (public member function)[edit] | |
Modifiers | |
| shrinks the view by moving its start forward (public member function)[edit] | |
| shrinks the view by moving its end backward (public member function)[edit] | |
| swaps the contents (public member function)[edit] | |
Operations | |
| copies characters (public member function)[edit] | |
| returns a substring (public member function)[edit] | |
| compares two views (public member function)[edit] | |
(C++20) | checks if the string view starts with the given prefix (public member function)[edit] |
(C++20) | checks if the string view ends with the given suffix (public member function)[edit] |
(C++23) | checks if the string view contains the given substring or character (public member function)[edit] |
| find characters in the view (public member function)[edit] | |
| find the last occurrence of a substring (public member function)[edit] | |
| find first occurrence of characters (public member function)[edit] | |
| find last occurrence of characters (public member function)[edit] | |
| find first absence of characters (public member function)[edit] | |
| find last absence of characters (public member function)[edit] | |
Constants | |
[static] | special value. The exact meaning depends on the context (public static member constant)[edit] |
(C++17)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20) | lexicographically compares two string views (function template)[edit] |
Input/output | |
(C++17) | performs stream output on string views (function template)[edit] |
Defined in inline namespace std::literals::string_view_literals | |
(C++17) | creates a string view of a character array literal (function)[edit] |
| hash support for string views (class template specialization)[edit] |
template<class CharT,class Traits> inlineconstexprbool | (since C++20) | |
This specialization ofranges::enable_borrowed_range makesbasic_string_view satisfyborrowed_range.
template<class CharT,class Traits> inlineconstexprbool | (since C++20) | |
This specialization ofranges::enable_view makesbasic_string_view satisfyview.
Deduction guides | (since C++20) |
It is the programmer's responsibility to ensure thatstd::string_view does not outlive the pointed-to character array:
std::string_view good{"a string literal"};// "Good" case: `good` points to a static array.// String literals reside in persistent data storage. std::string_view bad{"a temporary string"s};// "Bad" case: `bad` holds a dangling pointer since the std::string temporary,// created by std::operator""s, will be destroyed at the end of the statement.
Specializations ofstd::basic_string_view are already trivially copyable types in all existing implementations, even before the formal requirement introduced in C++23.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_string_view | 201606L | (C++17) | std::string_view |
201803L | (C++20) | ConstexprIterator | |
__cpp_lib_string_contains | 202011L | (C++23) | contains |
Output:
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The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3203 | C++17 | only pointers, iterators, and references returned from the member functions of basic_string_view might be invalidated | all pointers, iterators, and references to elements of basic_string_viewmay be invalidated |
| stores and manipulates sequences of characters (class template)[edit] | |
| concatenates two strings, a string and achar, or a string andstring_view (function template)[edit] | |
(C++20) | a non-owning view over a contiguous sequence of objects (class template)[edit] |
(C++11) | references a temporary array created inlist-initialization (class template)[edit] |
