Index: libcxx/include/sstream
===================================================================
--- libcxx/include/sstream
+++ libcxx/include/sstream
@@ -41,6 +41,7 @@
     // [stringbuf.members] Member functions:
     basic_string<char_type, traits_type, allocator_type> str() const;
     void str(const basic_string<char_type, traits_type, allocator_type>& s);
+    basic_string_view<char_type, traits_type> view() const noexcept; // C++20
 
 protected:
     // [stringbuf.virtuals] Overridden virtual functions:
@@ -92,6 +93,7 @@
     basic_stringbuf<char_type, traits_type, allocator_type>* rdbuf() const;
     basic_string<char_type, traits_type, allocator_type> str() const;
     void str(const basic_string<char_type, traits_type, allocator_type>& s);
+    basic_string_view<char_type, traits_type> view() const noexcept; // C++20
 };
 
 template <class charT, class traits, class Allocator>
@@ -132,6 +134,7 @@
     basic_stringbuf<char_type, traits_type, allocator_type>* rdbuf() const;
     basic_string<char_type, traits_type, allocator_type> str() const;
     void str(const basic_string<char_type, traits_type, allocator_type>& s);
+    basic_string_view<char_type, traits_type> view() const noexcept; // C++20
 };
 
 template <class charT, class traits, class Allocator>
@@ -172,6 +175,7 @@
     basic_stringbuf<char_type, traits_type, allocator_type>* rdbuf() const;
     basic_string<char_type, traits_type, allocator_type> str() const;
     void str(const basic_string<char_type, traits_type, allocator_type>& str);
+    basic_string_view<char_type, traits_type> view() const noexcept; // C++20
 };
 
 template <class charT, class traits, class Allocator>
@@ -191,6 +195,7 @@
 #include <istream>
 #include <ostream>
 #include <string>
+#include <string_view>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -252,6 +257,7 @@
     // [stringbuf.members] Member functions:
     string_type str() const;
     void str(const string_type& __s);
+    basic_string_view<char_type, traits_type> view() const noexcept; // C++20
 
 protected:
     // [stringbuf.virtuals] Overridden virtual functions:
@@ -446,15 +452,7 @@
 basic_string<_CharT, _Traits, _Allocator>
 basic_stringbuf<_CharT, _Traits, _Allocator>::str() const
 {
-    if (__mode_ & ios_base::out)
-    {
-        if (__hm_ < this->pptr())
-            __hm_ = this->pptr();
-        return string_type(this->pbase(), __hm_, __str_.get_allocator());
-    }
-    else if (__mode_ & ios_base::in)
-        return string_type(this->eback(), this->egptr(), __str_.get_allocator());
-    return string_type(__str_.get_allocator());
+    return string_type(this->view(), __str_.get_allocator());
 }
 
 template <class _CharT, class _Traits, class _Allocator>
@@ -490,6 +488,21 @@
     }
 }
 
+template <class _CharT, class _Traits, class _Allocator>
+basic_string_view<_CharT, _Traits>
+basic_stringbuf<_CharT, _Traits, _Allocator>::view() const noexcept
+{
+    if (__mode_ & ios_base::out)
+    {
+        if (__hm_ < this->pptr())
+            __hm_ = this->pptr();
+        return basic_string_view<_CharT, _Traits>(this->pbase(), __hm_ - this->pbase());
+    }
+    else if (__mode_ & ios_base::in)
+        return basic_string_view<_CharT, _Traits>(this->eback(), this->egptr() - this->eback());
+    return basic_string_view<_CharT, _Traits>();
+}
+
 template <class _CharT, class _Traits, class _Allocator>
 typename basic_stringbuf<_CharT, _Traits, _Allocator>::int_type
 basic_stringbuf<_CharT, _Traits, _Allocator>::underflow()
@@ -693,6 +706,10 @@
     void str(const string_type& __s) {
         __sb_.str(__s);
     }
+    _LIBCPP_INLINE_VISIBILITY
+    basic_string_view<char_type, traits_type> view() const noexcept {
+        return __sb_.view();
+    }
 };
 
 template <class _CharT, class _Traits, class _Allocator>
@@ -774,6 +791,10 @@
     void str(const string_type& __s) {
         __sb_.str(__s);
     }
+    _LIBCPP_INLINE_VISIBILITY
+    basic_string_view<char_type, traits_type> view() const noexcept {
+        return __sb_.view();
+    }
 };
 
 template <class _CharT, class _Traits, class _Allocator>
@@ -854,6 +875,10 @@
     void str(const string_type& __s) {
         __sb_.str(__s);
     }
+    _LIBCPP_INLINE_VISIBILITY
+    basic_string_view<char_type, traits_type> view() const noexcept {
+        return __sb_.view();
+    }
 };
 
 template <class _CharT, class _Traits, class _Allocator>