From aab4a1bfa2c3850a3bd83d68976d6d4b6a106648 Mon Sep 17 00:00:00 2001
From: sunmy <7743179+sun_mengyue@user.noreply.gitee.com>
Date: Wed, 9 Jun 2021 21:49:07 +0800
Subject: [PATCH] using static constexpr char array as default format

---
 include/fmt/chrono.h | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 163f2e4e..cf3bd08c 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -451,24 +451,16 @@ FMT_END_DETAIL_NAMESPACE
 template <typename Char, typename Duration>
 struct formatter<std::chrono::time_point<std::chrono::system_clock, Duration>,
                  Char> : formatter<std::tm, Char> {
-  FMT_CONSTEXPR FMT_INLINE void generate_default_spec(char) {
-    this->specs = {"%Y-%m-%d %H:%M:%S", 17};
-  }
-  FMT_CONSTEXPR FMT_INLINE void generate_default_spec(wchar_t) {
-    this->specs = {L"%Y-%m-%d %H:%M:%S", 17};
-  }
-
   template <typename ParseContext>
   FMT_CONSTEXPR auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
     auto it = ctx.begin();
     if (it != ctx.end() && *it == ':') ++it;
     auto end = it;
     while (end != ctx.end() && *end != '}') ++end;
-    if (end == it) {
-      generate_default_spec(typename ParseContext::char_type{});
-    } else {
+    if (end == it)
+      this->specs = {default_spec, 17};
+    else
       this->specs = {it, detail::to_unsigned(end - it)};
-    }
     return end;
   }
 
@@ -478,6 +470,10 @@ struct formatter<std::chrono::time_point<std::chrono::system_clock, Duration>,
     std::tm time = localtime(val);
     return formatter<std::tm, Char>::format(time, ctx);
   }
+  
+  static constexpr Char default_spec[] = {'%', 'Y', '-', '%', 'm', '-',
+                                          '%', 'd', ' ', '%', 'H', ':',
+                                          '%', 'M', ':', '%', 'S'};
 };
 
 template <typename Char> struct formatter<std::tm, Char> {