[boost] [date_time] Problem compiling is_leap_year

From: Richard Hadsell (hadsell_at_[hidden])
Date: 2007-05-02 10:15:51

Using g++ 3.4.4 (on 64-bit Linux) my source won't compile 
gregorian_calendar_base<>::is_leap_year.  The problem stems from the '%' 
operator with mixed types.  My code includes (unfortunately) a class 
that has arithmetic operators with most of the integer and 
floating-point types on the left, constructors from those types, and 
conversion operators to those types.  The compiler finds the ambiguity 
and can't decide between the built-in operator%(int, int) and all the 
other possibilities with my nasty class's '%' operators.

I fixed the problem in gregorian_calendar.ipp by casting 'year' to 'int' 
in 'is_leap_year'.  This is the diff:

diff -u -r1.1.1.1 gregorian_calendar.ipp
--- boost/date_time/gregorian_calendar.ipp      27 Apr 2007 17:10:19 -0000      1.1.1.1
+++ boost/date_time/gregorian_calendar.ipp      2 May 2007 13:59:31 -0000
@@ -164,7 +164,7 @@
   gregorian_calendar_base<ymd_type_,date_int_type_>::is_leap_year(year_type year) 
   {
     //divisible by 4, not if divisible by 100, but true if divisible by 400
-    return (!(year % 4))  && ((year % 100) || (!(year % 400)));
+    return (!(static_cast<int>(year) % 4))  && ((static_cast<int>(year) % 100) || (!(static_cast<int>(year) % 400)));
   }
   
   //! Calculate the last day of the month

We have had this problem since starting to use the date_time library in 
1.32.0.  The user was not interested in reporting it, and I hoped 
someone else would report it.  However, that has not happened, so here 
it is.  It would be nice to see it get into the next release.

BTW, we had some other similar problems, which we fixed by changing a 
few casts, but they have not reproduced themselves in 1.34.0 beta.  
Perhaps they were only problems for some other compiler, which we are no 
longer using.

-- 
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