esp32 __attribute__ ((packed))

 
typedef struct
{
	uint8_t type;
	uint8_t subType;
	uint16_t len; //network byte order:    len[0] high byte, len[1] low byte for 16bit length
	uint16_t sn;
    char cc;
}__attribute__ ((packed)) SESComHdr;

　　sizeof 输出7

typedef struct
{
uint8_t type;
uint8_t subType;
uint16_t len; //network byte order: len[0] high byte, len[1] low byte for 16bit length
uint16_t sn;
char cc;
}__attribute__ ((aligned(4))) SESComHdr;

输出8

 

typedef struct
{
uint8_t type;
uint8_t subType;
uint16_t len; //network byte order: len[0] high byte, len[1] low byte for 16bit length
uint16_t sn;
char cc;
}__attribute__ ((aligned(8))) SESComHdr;

sizeof 还是8