Fix compiler warnings for MSVCv1.4.3

Fixes #62. This fixes compiler warnings that are raised by MSVC.

In one case the code that was warned about was never executed, but
this compiles it out in that case to silence the warning.

1 files changed, 27 insertions, 7 deletions

diff --git a/include/cxxopts.hpp b/include/cxxopts.hpp
index ff17ec4..fe7d8ef 100644
--- a/include/cxxopts.hpp
+++ b/include/cxxopts.hpp
@@ -448,14 +448,14 @@ namespace cxxopts
         {
           if (negative)
           {
-            if (u > U(-std::numeric_limits<T>::min()))
+            if (u > static_cast<U>(-std::numeric_limits<T>::min()))
             {
               throw argument_incorrect_type(text);
             }
           }
           else
           {
-            if (u > std::numeric_limits<T>::max())
+            if (u > static_cast<U>(std::numeric_limits<T>::max()))
             {
               throw argument_incorrect_type(text);
             }
@@ -479,6 +479,23 @@ namespace cxxopts
       }
     }
 
+    template <typename R, typename T>
+    R
+    checked_negate(T&& t, const std::string&, std::true_type)
+    {
+      // if we got to here, then `t` is a positive number that fits into
+      // `R`. So to avoid MSVC C4146, we first cast it to `R`.
+      // See https://github.com/jarro2783/cxxopts/issues/62 for more details.
+      return -static_cast<R>(t);
+    }
+
+    template <typename R, typename T>
+    T
+    checked_negate(T&&, const std::string& text, std::false_type)
+    {
+      throw argument_incorrect_type(text);
+    }
+
     template <typename T>
     void
     integer_parser(const std::string& text, T& value)
@@ -537,11 +554,14 @@ namespace cxxopts
 
       if (negative)
       {
-        if (!is_signed)
-        {
-          throw argument_incorrect_type(text);
-        }
-        value = -result;
+        value = checked_negate<T>(result,
+          text,
+          std::integral_constant<bool, is_signed>());
+        //if (!is_signed)
+        //{
+        //  throw argument_incorrect_type(text);
+        //}
+        //value = -result;
       }
       else
       {