sa_family_t should be an unsigned integer. Windows头文件不符合该标准。Winsock.h定义sockaddr结构如下：

struct sockaddr {
        u_short sa_family;              /* address family */
        char    sa_data[14];            /* up to 14 bytes of direct address */
};

因此，要编译代码，您需要自己键入def sa_family_t。

如果有人得到了这个答案，并在Linux下寻找sa_family_t;，它在这里定义：
https://github.com/torvalds/linux/blob/1a5304fecee523060f26e2778d9d8e33c0562df3/include/linux/socket.h#L28

typedef __kernel_sa_family_t    sa_family_t;

__kernel_sa_family_t的定义如下：
https://github.com/torvalds/linux/blob/1a5304fecee523060f26e2778d9d8e33c0562df3/include/uapi/linux/socket.h#L10

typedef unsigned short __kernel_sa_family_t;

所以最终，sa_family_t是unsigned short，即2个字节。这使得整个struct sockaddr达到了16个字节：

struct sockaddr {
    sa_family_t sa_family;  // unsigned short
    char        sa_data[14];