Add wchar_t overload of format_to_n (#764)

include/fmt/format.h

@@ -3526,6 +3526,13 @@ inline OutputIt vformat_to(OutputIt out, string_view format_str,
   typedef output_range<OutputIt, char> range;
   return vformat_to<arg_formatter<range>>(range(out), format_str, args);
 }
+template <typename OutputIt, typename... Args>
+inline OutputIt vformat_to(
+    OutputIt out, wstring_view format_str,
+    typename format_args_t<OutputIt, wchar_t>::type args) {
+  typedef output_range<OutputIt, wchar_t> range;
+  return vformat_to<arg_formatter<range>>(range(out), format_str, args);
+}
 
 /**
  \rst
@@ -3578,12 +3585,20 @@ struct format_to_n_result {
  */
 template <typename OutputIt, typename... Args>
 inline format_to_n_result<OutputIt> format_to_n(
-    OutputIt out, std::size_t n, string_view format_str, const Args & ... args) {
+    OutputIt out, std::size_t n, string_view format_str, const Args &... args) {
   typedef internal::truncating_iterator<OutputIt> It;
   auto it = vformat_to(It(out, n), format_str,
       make_format_args<typename format_context_t<It>::type>(args...));
   return {it.base(), it.count()};
 }
+template <typename OutputIt, typename... Args>
+inline format_to_n_result<OutputIt> format_to_n(
+    OutputIt out, std::size_t n, wstring_view format_str, const Args &... args) {
+  typedef internal::truncating_iterator<OutputIt> It;
+  auto it = vformat_to(It(out, n), format_str,
+      make_format_args<typename format_context_t<It, wchar_t>::type>(args...));
+  return {it.base(), it.count()};
+}
 
 inline std::string vformat(string_view format_str, format_args args) {
   memory_buffer buffer;

test/format-test.cc

@@ -1525,6 +1525,15 @@ TEST(FormatTest, FormatToN) {
   EXPECT_EQ("foox", fmt::string_view(buffer, 4));
 }
 
+TEST(FormatTest, WideFormatToN) {
+  wchar_t buffer[4];
+  buffer[3] = L'x';
+  auto result = fmt::format_to_n(buffer, 3, L"{}", 12345);
+  EXPECT_EQ(5u, result.size);
+  EXPECT_EQ(buffer + 3, result.out);
+  EXPECT_EQ(L"123x", fmt::wstring_view(buffer, 4));
+}
+
 #if FMT_USE_CONSTEXPR
 struct test_arg_id_handler {
   enum result { NONE, EMPTY, INDEX, NAME, ERROR };