.../27_io/basic_ostream/print/buffered.cc | 90 +++++
.../format/functions/format_to_ostreambuf.cc | 340 ++++++++++++++++++
2 files changed, 430 insertions(+)
create mode 100644 libstdc++-v3/testsuite/27_io/basic_ostream/print/buffered.cc
create mode 100644
libstdc++-v3/testsuite/std/format/functions/format_to_ostreambuf.cc
diff --git a/libstdc++-v3/testsuite/27_io/basic_ostream/print/buffered.cc
b/libstdc++-v3/testsuite/27_io/basic_ostream/print/buffered.cc
new file mode 100644
index 00000000000..04ef159db39
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/basic_ostream/print/buffered.cc
@@ -0,0 +1,90 @@
+// { dg-additional-options "-lstdc++exp" { target { *-*-mingw* } } }
+// { dg-do run { target c++23 } }
+
+#include <sstream>
+#include <algorithm>
+#include <testsuite_hooks.h>
+
+struct ThrowingFormat
+{
+ std::string val;
+ bool throw_from_format = false;
+};
+
+template<>
+struct std::formatter<ThrowingFormat, char>
+{
+ constexpr
+ std::format_parse_context::iterator
+ parse(std::format_parse_context& ctx) const
+ { return ctx.begin(); }
+
+ template<typename Out>
+ Out
+ format(const ThrowingFormat& t, std::basic_format_context<Out, char>& fc)
const
+ {
+ if (t.throw_from_format)
+ throw std::logic_error("Formatting stopped");
+ return std::ranges::copy(t.val, fc.out()).out;
+ }
+};
+
+void
+test_throwing()
+{
+ std::string s;
+ s.reserve(100);
+ std::ostringstream out(std::move(s));
+ ThrowingFormat tf1{std::string(500, 'a'), false}, tf2{std::string(500, 'b'),
true};
+
+ try
+ {
+ std::print(out, "{} {}", tf1, tf2);
+ VERIFY(false);
+ } catch (...) {
+ VERIFY(true);
+ }
+ VERIFY( out.view().empty() );
+}
+
+struct MixedFormat
+{
+ std::ostream* out;
+ std::string val;
+};
+
+template<>
+struct std::formatter<MixedFormat, char>
+{
+ constexpr
+ std::format_parse_context::iterator
+ parse(std::format_parse_context& ctx) const
+ { return ctx.begin(); }
+
+ template<typename Out>
+ Out
+ format(const MixedFormat& t, std::basic_format_context<Out, char>& fc) const
+ {
+ if (t.out)
+ *t.out << "<<[" << t.val << "]";
+ return std::ranges::copy(t.val, fc.out()).out;
+ }
+};
+
+void
+test_interleaved()
+{
+ std::string s;
+ s.reserve(100);
+ std::ostringstream out(std::move(s));
+ MixedFormat mf1{&out, "abc"}, mf2{&out, "DEF"};
+
+ std::print(out, "f[{}]f[{}]", mf1, mf2);
+ VERIFY( out.view() == "<<[abc]<<[DEF]f[abc]f[DEF]" );
+}
+
+int main()
+{
+ test_throwing();
+ test_interleaved();
+}
diff --git
a/libstdc++-v3/testsuite/std/format/functions/format_to_ostreambuf.cc
b/libstdc++-v3/testsuite/std/format/functions/format_to_ostreambuf.cc
new file mode 100644
index 00000000000..1292057ff5c
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/format/functions/format_to_ostreambuf.cc
@@ -0,0 +1,340 @@
+// { dg-do run { target c++20 } }
+
+#include <format>
+#include <sstream>
+#include <string>
+#include <testsuite_hooks.h>
+
+template<std::streamsize BufSize>
+struct ShortWriteStreambuf : std::streambuf
+{
+ std::string data;
+
+ std::streamsize
+ xsputn(const char_type* s, std::streamsize n) override
+ {
+ std::streamsize limit = std::max<std::streamsize>(0, BufSize -
data.size());
+ std::streamsize to_write = std::min(n, limit);
+ if (to_write > 0)
+ data.append(s, to_write);
+ return to_write;
+ }
+
+ int_type
+ overflow(int_type c) override
+ {
+ if (data.size() < BufSize)
+ {
+ data.push_back(traits_type::to_char_type(c));
+ return c;
+ }
+ return traits_type::eof();
+ }
+};
+
+bool
+check_suffix(std::string_view s, size_t n, char c)
+{
+ if (s.size() < n)
+ return false;
+
+ s.remove_prefix(s.size() - n);
+ for (char v : s)
+ if (v != c)
+ return !n;
+ else if (!n)
+ return false;
+ else
+ --n;
+ return !n;
+}
+
+void
+test_format_to()
+{
+ {
+ std::ostringstream os;
+ std::format_to(std::ostreambuf_iterator<char>(os), "{}", 42);
+ VERIFY( os.view() == "42" );
+ }
+
+ {
+ std::ostringstream os;
+ std::string big(800, 'y');
+ std::format_to(std::ostreambuf_iterator<char>(os), "{}", big);
+ VERIFY( check_suffix(os.view(), 800, 'y') );
+ }
+
+ {
+ std::ostringstream os;
+ std::string part(700, 'P');
+ std::format_to(std::ostreambuf_iterator<char>(os),
+ "{}{}{}", part, part, part);
+ VERIFY( check_suffix(os.view(), 2100, 'P') );
+ }
+
+ {
+ std::ostringstream os;
+ std::string body(400, 'B');
+ std::format_to(std::ostreambuf_iterator<char>(os),
+ "header-{}-footer", body);
+
+ std::string_view sv = os.view();
+ VERIFY( sv.starts_with("header-") );
+ sv.remove_prefix(7);
+ VERIFY( sv.ends_with("-footer") );
+ sv.remove_suffix(7);
+ VERIFY( check_suffix(sv, 400, 'B') );
+ }
+}
+
+void
+test_format_to_n()
+{
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 1, "{}", "A");
+ VERIFY( res.size == 1 );
+ VERIFY( os.view() == "A" );
+ }
+
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 1, "{}", "AAA");
+ VERIFY( res.size == 3 );
+ VERIFY( os.view() == "A" );
+ }
+
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 3, "{}", "hello");
+ VERIFY( res.size == 5 );
+ VERIFY( os.view() == "hel" );
+ }
+
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 10, "{}", std::string(100, 'x'));
+ VERIFY( res.size == 100 );
+ VERIFY( check_suffix(os.view(), 10, 'x') );
+ }
+
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 10, "{}", std::string(1000, 'x'));
+ VERIFY( res.size == 1000 );
+ VERIFY( check_suffix(os.view(), 10, 'x') );
+ }
+
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 256, "{}", std::string(1000, 'x'));
+ VERIFY( res.size == 1000 );
+ VERIFY( check_suffix(os.view(), 256, 'x') );
+ }
+
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 257, "{}", std::string(1000, 'x'));
+ VERIFY( res.size == 1000 );
+ VERIFY( check_suffix(os.view(), 257, 'x') );
+ }
+
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 8, "{}{}{}", "AAAA", "BBBB", "CCCC");
+ VERIFY( res.size == 12 );
+ VERIFY( os.view() == "AAAABBBB" );
+ }
+
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 2, "{}{}", "AAAA", "BBBB");
+ VERIFY( res.size == 8 );
+ VERIFY( os.view() == "AA" );
+ }
+
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 8, "{}{}", "AAAA", "BBBB");
+ VERIFY( res.size == 8 );
+ VERIFY( os.view() == "AAAABBBB" );
+ }
+
+ {
+ std::string big(257, 'A');
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 257, "{}", big);
+ VERIFY( res.size == 257 );
+ std::string_view sv = os.view();
+ VERIFY( os.view() == big );
+ }
+
+ {
+ std::string big(300, 'A');
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 257, "{}", big);
+ VERIFY( res.size == 300 );
+ VERIFY( check_suffix(os.view(), 257, 'A') );
+ }
+}
+
+void
+test_format_to_n_padding()
+{
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 3, "{:>10}", "hello");
+ VERIFY( res.size == 10 );
+ VERIFY( os.view().size() == 3 );
+ }
+
+ {
+ std::ostringstream os;
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 3, "{:.5}", std::string(100, 'z'));
+ VERIFY( res.size == 5 );
+ VERIFY( check_suffix(os.view(), 3, 'z') );
+ }
+}
+
+void
+test_format_to_n_prefilled()
+{
+ // Pre-filled ostringstream: after seekp(0) the streambuf has a put
+ // area pointing into existing data. This exercises the
+ // _M_use_put_area code path combined with format_to_n truncation.
+ {
+ std::string init(100, 'Z');
+ std::ostringstream os(init);
+ os.seekp(0);
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 5, "{}", "1234567890");
+ VERIFY( res.size == 10 );
+ VERIFY( os.view().substr(0, 10) == "12345ZZZZZ" );
+ VERIFY( check_suffix(os.view(), 90, 'Z') );
+ }
+ {
+ std::string init(100, 'Z');
+ std::ostringstream os(init);
+ os.seekp(0);
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 8, "{:=>15}", "1234567890");
+ VERIFY( res.size == 15 );
+ VERIFY( os.view().substr(0, 10) == "=====123ZZ" );
+ VERIFY( check_suffix(os.view(), 90, 'Z') );
+ }
+ {
+ std::string init(100, 'Z');
+ std::ostringstream os(init);
+ os.seekp(0);
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 3, "{}", 12345);
+ VERIFY( res.size == 5 );
+ VERIFY( os.view().substr(0, 10) == "123ZZZZZZZ" );
+ VERIFY( check_suffix(os.view(), 90, 'Z') );
+ }
+ {
+ std::string init(100, 'Z');
+ std::ostringstream os(init);
+ os.seekp(0);
+ auto res = std::format_to_n(std::ostreambuf_iterator<char>(os),
+ 7, "{:=>10}", 12345);
+ VERIFY( res.size == 10 );
+ VERIFY( os.view().substr(0, 10) == "=====12ZZZ" );
+ VERIFY( check_suffix(os.view(), 90, 'Z') );
+ }
+}
+
+void
+test_write_failure()
+{
+ const std::string payload(20, 'Z');
+
+ {
+ ShortWriteStreambuf<20> buf;
+ auto it = std::ostreambuf_iterator<char>(&buf);
+ auto res = std::format_to(it, "{}", payload);
+ VERIFY( !res.failed() );
+ VERIFY( check_suffix(buf.data, 20, 'Z') );
+ }
+
+ {
+ ShortWriteStreambuf<19> buf;
+ auto it = std::ostreambuf_iterator<char>(&buf);
+ auto res = std::format_to(it, "{}", payload);
+ VERIFY( res.failed() );
+ VERIFY( check_suffix(buf.data, 19, 'Z') );
+ }
+
+ {
+ ShortWriteStreambuf<10> buf;
+ auto it = std::ostreambuf_iterator<char>(&buf);
+ auto res = std::format_to_n(it, 10, "{}", payload);
+ VERIFY( !res.out.failed() );
+ VERIFY( res.size == 20 );
+ VERIFY( check_suffix(buf.data, 10, 'Z') );
+ }
+
+ {
+ ShortWriteStreambuf<10> buf;
+ auto it = std::ostreambuf_iterator<char>(&buf);
+ auto res = std::format_to_n(it, 11, "{}", payload);
+ VERIFY( res.out.failed() );
+ VERIFY( res.size == 20 );
+ VERIFY( check_suffix(buf.data, 10, 'Z') );
+ }
+
+ {
+ ShortWriteStreambuf<100> buf;
+ auto it = std::ostreambuf_iterator<char>(&buf);
+ auto res = std::format_to(it, "{}", std::string(300, 'Y'));
+ VERIFY( res.failed() );
+ VERIFY( buf.data.size() == 100 );
+ VERIFY( check_suffix(buf.data, 100, 'Y') );
+ }
+ // format_to_n after write failure: size must still be the total
+ // number of characters that would have been produced.
+ {
+ ShortWriteStreambuf<50> buf;
+ auto it = std::ostreambuf_iterator<char>(&buf);
+ auto res = std::format_to_n(it, 100,
+ "{}{}{}",
+ std::string(20, 'A'),
+ std::string(30, 'B'),
+ std::string(40, 'C'));
+ // The first two arguments fill the buffer (20 + 30 == 50).
+ // The third argument (40 C's) triggers write failure and the
+ // remaining chars must still be counted in res.size.
+ VERIFY( res.out.failed() );
+ VERIFY( res.size == 90 );
+
+ std::string_view sv = buf.data;
+ VERIFY( buf.data.size() == 50 );
+ VERIFY( check_suffix(sv, 30, 'B') );
+ sv.remove_suffix(30);
+ VERIFY( check_suffix(sv, 20, 'A') );
+ }
+}
+
+int main()
+{
+ test_format_to();
+ test_format_to_n();
+ test_format_to_n_padding();
+ test_format_to_n_prefilled();
+ test_write_failure();
+}
--
2.55.0
