c++ - How would I portably implement aligned stack storage in C++03? -

in c++03 code, how portably implement unsigned char[sizeof(t)] buffer has same size , alignment of given type t?

for example:

template<class t> void test() {     unsigned char buffer[sizeof(t)];   // <----- how ensure aligned?     if (some_condition())     {         t *const obj = new(buffer) t();         // ...         obj->~t();     }     else { /* use 'buffer' else */ } } 

is possible, or forced use compiler extensions in order implement this?

in guru of week #28 column, herb sutter uses union it's less robust boost's efforts.

boost's aligned_storage solves gory details you. if @ implementation, you'll see uses mscv's __alignof or gcc's __alignof__ template: type_with_alignment.

from own codebase, once used (derived gotw link above):

#if defined(_msc_full_ver) && (_msc_full_ver >= 150020706) #  pragma warning(push) #  pragma warning(disable: 4371) #endif // #if (defined(_msc_full_ver) && (_msc_full_ver >= 150020706)       union alignedstorage       {         char        storage[sizeof(t)];         int16       dummy0;         int32       dummy1;         int64       dummy2;         float       dummy3;         double      dummy4;         long double dummy5;         void        (*dummy6)();         struct      dummy7;         int         dummy7::*dummy8; #if defined(_msc_full_ver) && (_msc_full_ver >= 140050215) #  pragma warning(push) #  pragma warning(disable: 4121) #endif // #if (defined(_msc_full_ver) && (_msc_full_ver >= 140050215)         int         (dummy7::*dummy9)(int); #if defined(_msc_full_ver) && (_msc_full_ver >= 140050215) #  pragma warning(pop) #endif // #if (defined(_msc_full_ver) && (_msc_full_ver >= 140050215)        }; // alignedstorage #if defined(_msc_full_ver) && (_msc_full_ver >= 150020706) #  pragma warning(pop) #endif // #if (defined(_msc_full_ver) && (_msc_full_ver >= 150020706) 

these days rely on boost since covers many more corner cases , compiler specificities