问为什么std：：std流不能与std::string_view一起工作？

EN

explicit basic_stringstream( std::basic_string<CharT,Traits,Allocator>&& str,
                             std::ios_base::openmode mode = 
                             std::ios_base::in | std::ios_base::out );

std::string str("Hello ");                            // std::string
constexpr char c_str[] = "Hey and how are you ";      // C-string
std::string_view sv(c_str);                           // std::string_view

std::stringstream ss1(str);                           // from a std::string
std::stringstream ss3(std::move(std::string(c_str))); // from a C-string
std::stringstream ss2(std::move(std::string(sv)));    // from a std::string_view

std::string str("Hello ");                          // std::string
constexpr char c_str[] = "Hey and how are you ";    // C-string
std::string_view sv(c_str);                         // std::string_view

// 1. Construct a `std::stringstream` from a `std::string`. This is
// constructor #3 from the link below: reference page for the
// `std::stringstream` constructors:
// https://en.cppreference.com/w/cpp/io/basic_stringstream/basic_stringstream
// - Open in mode `std::ios_base::app` as well in order to **append** all new
//   writes to the end of the stream! See link above **and**:
//   https://stackoverflow.com/a/8786212/4561887
std::stringstream ss1(str, 
    std::ios_base::in | std::ios_base::out | std::ios_base::app);
ss1 << "world.\n";  // since `std::ios_base::app` was used above, this 
                    // **appends** rather than **overwrites** the data in 
                    // the stringstream.
std::cout << ss1.str() << "\n";

// 2. Construct a `std::stringstream` from a `std::string_view`. This is also
// constructor #3 from the link above (passing in a `std::string), but we must
// first construct a `std::string` from the `std::string_view`. We are using
// constructor #10 from the `std::string` constructors shown here to create a
// `std::string` from a `std::string_view`:
// https://en.cppreference.com/w/cpp/string/basic_string/basic_string
// - See also the note about the `std::ios_base::app` mode above.
std::stringstream ss2b(std::move(std::string(sv)),
    std::ios_base::in | std::ios_base::out | std::ios_base::app);
ss2b << "today?\n";
std::cout << ss2b.str() << "\n";

// 3. Construct a `std::stringstream` from a C-string. This is also
// constructor #3 from the link above (passing in a `std::string), but we must
// first construct a `std::string` from the C-string. We are using
// constructor #5 from the `std::string` constructors shown here to create a
// `std::string` from a C-string (`const char*`):
// https://en.cppreference.com/w/cpp/string/basic_string/basic_string
// - See also the note about the `std::ios_base::app` mode above. Note that the
//   C-string is used to automatically, implicitly construct a `std::string`
//   here, I believe.
//
// implicit construction of `std::string` from `c_str`
std::stringstream ss3c(std::move(c_str),
    std::ios_base::in | std::ios_base::out | std::ios_base::app);
ss3c << "doing?\n";
std::cout << ss3c.str();
// explicit construction of `std::string` from `c_str`
std::stringstream ss3d(std::move(std::string(c_str)),
    std::ios_base::in | std::ios_base::out | std::ios_base::app);
ss3d << "doing?\n";
std::cout << ss3d.str();

Hello world.
Hey and how are you today?
Hey and how are you doing?
Hey and how are you doing?