sizeof (struct sockaddr) sizeof (struct sockaddr_in)

都是 16字节
实际上这两个结构可以直接相互转换的。
struct sockaddr {
u_short sa_family; /* address family */
char sa_data[14]; /* up to 14 bytes of direct address */
};

struct sockaddr_in {
short sin_family;
u_short sin_port;
struct in_addr sin_addr;
char sin_zero[8];
};

struct in_addr {
union {
struct { u_char s_b1,s_b2,s_b3,s_b4; } S_un_b;
struct { u_short s_w1,s_w2; } S_un_w;
u_long S_addr;
} S_un;

就看你sockaddr和sockaddr_in是不是有相同的元素了。