[Boost-bugs] [Boost C++ Libraries] #13614: padding related issue on VS2017 with boost::endian

Subject: [Boost-bugs] [Boost C++ Libraries] #13614: padding related issue on VS2017 with boost::endian
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2018-06-21 04:51:38

#13614: padding related issue on VS2017 with boost::endian
------------------------------+-------------------------
 Reporter:  imak@…            |      Owner:  Beman Dawes
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  endian
  Version:  Boost 1.67.0      |   Severity:  Problem
 Keywords:                    |
------------------------------+-------------------------
 On Visual Studio 2017 upd3, there seems to be some unexpected padding-
 related behaviour, shown below. The issue might not necessarily be a
 library 'bug', but I think it's worth looking at.

 {{{
 #!div style="font-size: 80%"
 Code highlighting:
   {{{#!c++
 #include <stdio.h>

 #include <boost/endian/arithmetic.hpp>
 using namespace boost::endian;

 #pragma pack(push, 1)

 struct Empty {};

 struct T1
 {
     big_uint16_t d;
     uint8_t d2;
 };

 struct T2
 {
     uint16_t d;
     uint8_t d2;
 };

 struct D0: T1 {} x0;          // sizeof(x0) evaluates to 3
 struct D1: T1, Empty {} x1;   // sizeof(x1) evaluates to 4  <- i think
 this should also be 3
 struct D2: T2, Empty {} x2;   // sizeof(x2) evaluates to 3

 // (uint8_t*)&x1.d2 - (uint8_t*)&x1.d   evaluates to 2 (i.e. big_uint16_t
 is itself not padded)
 //
 // - tested with a struct containing a char[2], this did not happen
 // - tested on various versions of g++ and clang, but this did not happen
 either.

 #pragma pack(pop)

 using namespace std;

 int main()
 {
     printf("%zu %zu %zu", sizeof(x0), sizeof(x1), sizeof(x2));

     return 0;
 }
   }}}
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac10/ticket/13614>
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