about pack and align for C/C++

http://msdn.microsoft.com/en-us/library/2e70t5y1(VS.80).aspx
#pragma
pack(  n  )
n : Valid values are 1, 2, 4, 8, and 16.the
alignment of a member will be on a boundary that is either a multiple of 
n
 or
a multiple of the size of the member
,
whichever is smaller.
The
default value for n
 is 8
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#pragma
pack(8)
struct ABCD
{
bool
b;
short s;
double d;
};
int
main()
{
cout << offsetof(ABCD,
b) << endl;
cout << offsetof(ABCD,
s) << endl;
cout << offsetof(ABCD,
d) << endl;
cout << sizeof(ABCD) << endl;
}
output
is:
0 
2
8
16
http://msdn.microsoft.com/en-us/library/83ythb65(VS.71).aspx
__declspec( align( n ) )
__declspec( align() ) ºÍ #pragma pack
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#define
CACHE_ALIGN 64 
// Force each structure to be
in a different cache line. 
struct
__declspec(align(CACHE_ALIGN)) CUSTINFOAA { 
DWORD
   dwCustomerID;     // Mostly read-only 
wchar_t
 szName[100];      // Mostly read-only 
// Force the following members to be in a different cache line. 
__declspec(align(CACHE_ALIGN)) 
  int
nBalanceDue;           // Read-write 
FILETIME
ftLastOrderDate;  // Read-write 
}; 
int
main()
{
cout <<
offsetof(CUSTINFOAA, dwCustomerID) << endl;
cout
<< offsetof(CUSTINFOAA, szName) << endl;
cout
<< offsetof(CUSTINFOAA, nBalanceDue) << endl;
cout << offsetof(CUSTINFOAA, ftLastOrderDate) <<
endl;
cout << sizeof(CUSTIN