关于Linux下SO_REUSEADDR的疑问？

//demo.cpp

#include <stdio.h>

#include <netdb.h>

#include <errno.h>

#include <string.h>

#include <unistd.h>

#include <linux/tcp.h>



int SockDemo()

{

	sockaddr_in in;

	memset(&in,'\0',sizeof(in));

	in.sin_family=AF_INET;

	in.sin_port=htons(8880);

	in.sin_addr.s_addr=INADDR_ANY;

	

	int reuse0=1;

	int serv=socket(AF_INET, SOCK_STREAM, 0);

	if (setsockopt(serv, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse0, sizeof(reuse0))==-1) return errno;

	if (bind(serv, (sockaddr*)&in, sizeof(sockaddr)) == -1) return errno;

	if (listen(serv, SOMAXCONN)==-1) return errno;

	

	int reuse1=1;

	int client=socket(AF_INET, SOCK_STREAM, 0);

	if (setsockopt(client, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse1, sizeof(reuse1))==-1) return errno;



	if (bind(client, (sockaddr*)&in, sizeof(sockaddr)) == -1) return errno;

	//****** 此处为报错 *****：errno=98, Address already in use.



	sleep(1);

	

	close(client);

	close(serv);

	return 0;

	

}



int main(int argc, char *argv[])

{

	int errcode=SockDemo();

	printf("errno=%d, %s.\n", errcode, strerror(errcode));

	return 0;

}