From e6b1e0fe584337e76b27b80e3831d7397aea33df Mon Sep 17 00:00:00 2001
From: Howard Hinnant <howard.hinnant@gmail.com>
Date: Mon, 24 Jul 2017 08:18:18 -0400
Subject: [PATCH] Allow read_unsigned to read 0 digits

* Will allow reading "optional" integers.
---
 date.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/date.h b/date.h
index 734b2e6..5876bed 100644
--- a/date.h
+++ b/date.h
@@ -5297,7 +5297,7 @@ read_signed(std::basic_istream<CharT, Traits>& is, unsigned m = 1, unsigned M =
         {
             if (c == '-' || c == '+')
                 (void)is.get();
-            auto x = static_cast<int>(read_unsigned(is, m, M));
+            auto x = static_cast<int>(read_unsigned(is, std::max(m, 1u), M));
             if (!is.fail())
             {
                 if (c == '-')
@@ -5306,7 +5306,8 @@ read_signed(std::basic_istream<CharT, Traits>& is, unsigned m = 1, unsigned M =
             }
         }
     }
-    is.setstate(std::ios::failbit);
+    if (m > 0)
+        is.setstate(std::ios::failbit);
     return 0;
 }