Printf get container

include/fmt/printf.h

@@ -480,11 +480,13 @@ OutputIt basic_printf_context<OutputIt, Char>::format() {
     }
     char_type c = *it++;
     if (it != end && *it == c) {
-      out = std::copy(start, it, out);
+      out = detail::write(
+          out, basic_string_view<Char>(start, detail::to_unsigned(it - start)));
       start = ++it;
       continue;
     }
-    out = std::copy(start, it - 1, out);
+    out = detail::write(out, basic_string_view<Char>(
+                                 start, detail::to_unsigned(it - 1 - start)));
 
     format_specs specs;
     specs.align = align::right;
@@ -596,7 +598,8 @@ OutputIt basic_printf_context<OutputIt, Char>::format() {
     // Format argument.
     out = visit_format_arg(ArgFormatter(out, specs, *this), arg);
   }
-  return std::copy(start, it, out);
+  return detail::write(
+      out, basic_string_view<Char>(start, detail::to_unsigned(it - start)));
 }
 
 template <typename Char>

test/printf-test.cc

@@ -619,10 +619,26 @@ TEST(PrintfTest, PrintfDetermineOutputSize) {
   const auto format_arg = "Hello";
   const auto expected_size = fmt::sprintf(format_string, format_arg).size();
 
-  EXPECT_EQ((truncated_printf_context(
+  EXPECT_EQ(expected_size,
+            (truncated_printf_context(
                  fmt::detail::truncating_iterator<backit>(it, 0), format_string,
                  fmt::make_format_args<truncated_printf_context>(format_arg))
                  .format()
-                 .count()),
-            expected_size);
+                 .count()));
+}
+
+TEST(PrintfTest, PrintfAppendToBuffer) {
+  using backit = std::back_insert_iterator<fmt::basic_memory_buffer<char>>;
+  using context = fmt::basic_printf_context<backit, char>;
+
+  const auto format_string = "%s";
+  const char* format_arg = "Hello";
+  fmt::basic_memory_buffer<char> buffer;
+  context(std::back_inserter(buffer), format_string,
+          fmt::make_format_args<context>(format_arg))
+      .format();
+
+  std::string result(std::begin(buffer), std::end(buffer));
+
+  EXPECT_EQ(std::string("Hello"), result);
 }