byte alignment

Byte alignment ：
If it takes N Bytes , His starting address must be N Integer multiple ; namely ： Initial address %N=0;
Structure alignment
The structure is aligned with the largest member ： Initial address %N=0;（ The starting address of the structure is an integer multiple of the widest member type ）

pragma pack（N）
When the space requirements are relatively high , Can pass #pragma pack（N） To change the alignment of structure members
e.g #pragma pack(1)
struct Test {
char b;
int a;
}
#pragma pack（）// Unalign

（1）#pragma pack（） You can set N Byte alignment （1,2,4,8 VC Compiler defaults 8）
N=min（ The maximum occupied bytes of structure members , Align bytes ）
Calculate the size of the structure as N Integer multiple

#prgma pack(1,2,4,8)
typedef struct
{
char a;
int b;
char ;
}
#pragma pack () The starting address of the structure is 4 Integer multiple （ namely Initial address %4 =0）
Total size of structure ：N = Min（ The largest member , Alignment parameters ）
yes N Integer multiple