std::string operator std::string_view

od C++20

constexpr operator std::basic_string_view<CharT, Traits>() const noexcept;

od C++17

operator std::basic_string_view<CharT, Traits>() const noexcept;

Returns a std::basic_string_view, constructed as if by

std::basic_string_view<CharT, Traits>(data(), size())

Parameters

(none)

Return value

A string view representing the entire contents of the string.

Complexity

Constant - O(1).

Exceptions

(none)

Notes

It is the programmer's responsibility to ensure that the resulting string view does not outlive the string.

std::string get_string();
int f(std::string_view sv);

int x = f(get_string()); // OK
std::string_view sv = get_string(); // Bad: holds a dangling pointer

Example

Main.cpp

#include <iostream>
#include <string>
#include <string_view>
 
void show_wstring_size(std::wstring_view wcstr_v)
{
  std::cout << wcstr_v.size() << " code points\n";
}
 
int main()
{
  std::string cppstr = "ラーメン";   // narrow string
  std::wstring wcstr = L"ラーメン";  // wide string
 
  // Implicit conversion from string to string_view
  // via std::string::operator string_view:
  std::string_view cppstr_v = cppstr;
 
  std::cout << cppstr_v << '\n'
            << cppstr_v.size() << " code units\n";
 
  // Implicit conversion from wstring to wstring_view
  // via std::wstring::operator wstring_view:
  show_wstring_size(wcstr);
}

Output

ラーメン
12 code units
4 code points