#pragma pack (push,1) and #pragma pack (POP)

This is the parameter setting for the compiler, for the structure byte alignment setting, #pragma pack is the alignment of the specified data in memory.

#pragma pack (n) Action: The C compiler will be aligned by N bytes.
#pragma pack () Effect: cancels custom byte alignment.

#pragma pack (push,1) function: means to set the original alignment of the stack, and set a new alignment to a byte alignment

#pragma pack (POP) Action: Restore Alignment State

As a result, adding push and pop allows alignment to revert to its original state, rather than the compiler default, which can be said to be better, but many times the difference is small

Such as:

#pragma pack (push)//Save alignment status

#pragma pack (4)//set to 4-byte alignment

Equivalent to #pragma pack (push,4)

#pragma  Pack (1)           action: Adjust the boundary alignment of the structure so that it aligns in one byte;< to align the struct with a 1-byte alignment >#pragma  pack () For example:#pragma Pack (1)struct  sample{Char  A; Double b;}; #pragma pack ()

Note: If you do not enclose #pragma pack (1) and #pragma pack (), sample is aligned by the compiler default (that is, the size of the largest member). That is, by 8 bytes (double), the sizeof (sample) ==16. Member Char a takes up 8 bytes (7 of which are empty bytes), and if #pragma pack (1) is used, sample is aligned to sizeof (sample) by 1 bytes ==9. (no empty bytes), more space saving, some fields and also can make the structure more easy to control.

#pragma pack (push,1) and #pragma pack (POP)