Use the right alignment for a buffer which is supposed to hold a struct in C++ -

suppose have struct, say

struct s {   double a, b;   ~s(); // s doesn't have pod }; 

such struct should typically have alignment of 8, size of largest contained type 8.

now imagine want declare placeholder struct hold value of s:

struct placeholder {   char bytes[ sizeof( s ) ]; }; 

now want place inside of class:

class user {   char somechar;   placeholder holder; public:   // don't mind hacky -- shows possible use   // that's not point of question   user() { new ( holder.bytes ) s; }   ~user() {  ( ( s * )( holder.bytes ) )->~s(); } }; 

problem is, placeholder aligned incorrectly within user. since compiler knows placeholder made of chars, not doubles, typically use alignment of 1.

is there way declare placeholder alignment matching of s in c++03? note s not pod type. understand c++11 has alignas, not universally available yet, i'd rather not count on if possible.

update: clarify, should work s - don't know contains.

i believe boost::aligned_storage may you're looking for. uses union trick in such way type doesn't matter (you use sizeof(yourtype) tell how align) make sure alignment works out properly.