"struct 형식 재정의" 에러

#include <winsock2.h>

struct sockaddr {
	unsigned short    sa_family;    /* address family, AF_xxx       */
	char              sa_data[14];  /* 14 bytes of protocol address */
}sockaddr;

struct sockaddr_in {
	short int          sin_family;  /* Address family               */
	unsigned short int sin_port;    /* Port number                  */
	struct in_addr     sin_addr;    /* Internet address             */
	unsigned char      sin_zero[8]; /* Same size as struct sockaddr */
}sockaddr_in;

/* Internet address (a structure for historical reasons) */
struct in_addr {
	unsigned long s_addr;
};

컴파일을 하게 되면
위에 제목처럼 에러가 나게 됩니다.
환경은
-----윈도우
-----비쥬얼C++

왜 이런 에러가 나는건가요?.