Subject: Re: [Boost-users] serilalization of union
From: Robert Ramey (ramey_at_[hidden])
Date: 2009-01-07 20:34:57
This is what boost variant serialization does.
Robert Ramey
Andrew Holden wrote:
> Robert Ramey wrote:
>> Steven Watanabe wrote:
>>> AMDG
>>>
>>> niranjan bangera wrote:
>>>> union myunion
>>>> {
>>>>
>>>> uint32_t a;
>>>> float t;
>>>>
>>>> template <class Archive>
>>>> void serialize(Archive & ar, const unsigned int file_version)
>>>> {
>>>>
>>>> ar & a;
>>>> ar & t;
>>>>
>>>> }
>>>
>>> This is undefined behavior. a and t cannot both be valid at the
>>> same time.
>>
>> LOL - makes me wonder if I'm even reading these emails.
>>
>> One could do try:
>>
>> struct myunion {
>> union {
>> uint32_t a;
>> float t;
>> } x;
>> operator (uint32_t &)(){ // i forget the exact casting operator
>> syntax return a;
>> }
>> operator(float &t)(){
>> return t;
>> }
>> template<class Archive>
>> void serialize(Archive & ar, const unsigned int file_version){
>> ar & binary_object(sizeof(x), &x);
>> }
>> };
>>
>> crude - but effective.
>>
>> Robert Ramey
>
> The best solutions would become more obvious if you know which type
> is valid at a higher level. For example, if you have a structure
> like this:
>
> struct UnionWrapper
> {
> myunion the_union;
> bool is_float; /* Set to true if and only if the float member
> is used */
>
> template <class Archive>
> void serialize (Archive &ar, unsigned int const version)
> {
> ar & is_float; /*Do this first so deserialization knows which
> union member to get. */
>
> if (is_float)
> {
> ar & the_union.t;
> }
> else
> {
> ar & the_union.a;
> }
> }
> };