逻辑上socket处于应用层与传输层之间。

ip,端口，协议，一起决定了网络的一个端点。

#include <iostream>#include "unp.h"int main(int argc, char** argv){    int sockfd;    int n;    char recvline[MAXLINE + 1];    struct sockaddr_in servaddr;    if (argc != 2)    {        err_quit("usage: a.out <IPaddress>");    }    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)    {        err_sys("socket error");    }    bzero(&servaddr, sizeof(servaddr));    servaddr.sin_family = AF_INET;    servaddr.sin_port   = htons(13); // daytime server    if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0)    {        err_quit("inet_pton error for %s", argv[1]);    }    if (connect(sockfd, (SA*)&servaddr, sizeof(servaddr)) < 0)    {        err_sys("connect error");    }    while ( (n = read(sockfd, recvline, MAXLINE)) > 0)    {        recvline[n] = 0; // null terminate        if (fputs(recvline, stdout) == EOF)        {            err_sys("fputs error");        }    }    if (n < 0)    {        err_sys("read error");    }    exit(0);}

ALL = daytimetcpcli daytimetcpsrv client server byteorderCFLAGS = -Wall -gall: ${ALL}daytimetcpcli.o: daytimetcpcli.cpp	g++ ${CFLAGS} -c daytimetcpcli.cpp -I ../lib -o daytimetcpcli.odaytimetcpcli: daytimetcpcli.o	g++ ${CFLAGS} daytimetcpcli.o ../libunp.a -I ../lib -o daytimetcpclidaytimetcpsrv.o: daytimetcpsrv.cpp	g++ ${CFLAGS} -c daytimetcpsrv.cpp -I ../lib -o daytimetcpsrv.odaytimetcpsrv: daytimetcpsrv.o	g++ ${CFLAGS} daytimetcpsrv.o ../libunp.a -I ../lib -o daytimetcpsrvclient.o: client.cpp	g++ ${CFLAGS} -c client.cpp -o client.o client: client.o	g++ ${CFLAGS} client.o -o clientserver.o: server.cpp	g++ ${CFLAGS} -c server.cpp -o server.oserver: server.o	g++ ${CFLAGS} server.o -o serverbyteorder.o: byteorder.cpp	g++ ${CFLAGS} -c byteorder.cpp -I ../lib -o byteorder.obyteorder: byteorder.o	g++ ${CFLAGS} byteorder.o -I ../lib -o byteorderclean:	rm *.o ${ALL}

UNIX网络编程1.1概述 1.2时间获取客户函数 1.4错误处理包裹函数