std::basic_string_view

The class template std::basic_string_view is a lightweight non-owning view of a constant contiguous character sequence.

basic_string_view is for observing text, not owning it. Copying a string view copies only the pointer/length pair, so it is cheap to pass by value, but the referenced characters must outlive the view.

# Declarations

template< class CharT, class Traits = std::char_traits<CharT> >
class basic_string_view;

(since C++17)

# Template parameters

# Semantic model

• A string view does not allocate and does not own storage.
• The viewed character range is constant; the view can be reseated or shortened, but it does not modify the underlying characters.
• Size is tracked explicitly, so a string view may refer to substrings and character ranges that are not null-terminated.
• The view is contiguous and tuple-free: element access, iteration, comparison, and search all operate directly on the referenced range.

# Example

#include <iostream>
#include <string_view>
 
int main()
{
    constexpr std::string_view unicode[]{"▀▄─", "▄▀─", "▀─▄", "▄─▀"};
 
    for (int y{}, p{}; y != 6; ++y, p = ((p + 1) % 4))
    {
        for (int x{}; x != 16; ++x)
            std::cout << unicode[p];
        std::cout << '\n';
    }
}

This is the central usage pattern: pass a cheap read-only view into existing character storage without copying the string data.

# Member types

iterator and const_iterator are the same type because basic_string_view views constant characters.

# Reference map

# Helper templates

• ranges::enable_borrowed_range<std::basic_string_view<CharT, Traits>> = true makes basic_string_view a borrowed range in C++20.
• ranges::enable_view<std::basic_string_view<CharT, Traits>> = true makes basic_string_view a view in C++20.

# Deduction guides

The class has deduction guides so construction from compatible character ranges can infer the CharT and Traits parameters.

# Notes

It is the programmer’s responsibility to ensure that the referenced characters outlive the view. A std::string_view can safely refer to a string literal, but it can easily dangle when bound to a temporary std::string.

Specializations of std::basic_string_view were already trivially copyable in practice before that guarantee became a formal requirement in C++23.

# Feature-test macros

# Defect reports

# See also

• std::basic_string
• std::span
• std::initializer_list
• list-initialization