Bug in boost::date_time::c_time::localtime(), boost::date_time::c_time::gmtime()

[Farid Zaripov <faridz@…>]

The code below fails on asserts on MSVC 8

    const std::time_t tt = std::time(0);
    std::tm tms;
    tms.tm_hour = 28;
    const std::tm * ptm = boost::date_time::c_time::localtime(&tt, &tms);
    assert(&tms == ptm);
    assert(28 != tms.tm_hour);

The proposed patch:

Index: c_time.hpp
===================================================================
--- c_time.hpp	(revision 56335)
+++ c_time.hpp	(working copy)
@@ -80,18 +80,20 @@
       inline
       static std::tm* localtime(const std::time_t* t, std::tm* result)
       {
-        result = std::localtime(t);
-        if (!result)
+        std::tm* const tmp = std::localtime(t);
+        if (!tmp)
           boost::throw_exception(std::runtime_error("could not convert calendar time to local time"));
+        *result = *tmp;
         return result;
       }
       //! requires a pointer to a user created std::tm struct
       inline
       static std::tm* gmtime(const std::time_t* t, std::tm* result)
       {
-        result = std::gmtime(t);
-        if (!result)
+        std::tm* const tmp = std::gmtime(t);
+        if (!tmp)
           boost::throw_exception(std::runtime_error("could not convert calendar time to UTC time"));
+        *result = *tmp;
         return result;
       }
 #if (defined(_MSC_VER) && (_MSC_VER >= 1400))

[Andrey Semashev]

Hmm... According to the docs the functions should return the pointer to tm passed as an argument, so technically this is a bug. However, I don't see a good rationale for this requirement as it only introduces unnecessary data copying. Also, this code is there for ages and no one has brought it up. Maybe we're better off correcting the docs. And a new, more C++-style interface might also be a good idea.

Do you have a rationale for this change? A motivating example, perhaps?

[Andrey Semashev]

(In [56548]) Refs #3470. Modified documentation for c_time functions to reflect the actual behavior.

[Andrey Semashev]

(In [56549]) Fixes #3470. Merged from trunk revision 56548.