read、write 与recv、send区别 gethostname

recv相对于read有什么区别呢？

其实它跟read函数功能一样，都可以从套接口缓冲区sockfd中取数据到buf,但是recv仅仅只能够用于套接口IO，并不能用于文件IO以及其它的IO，而read函数可以用于任何的IO；

recv函数相比read函数多了一个flags参数，通过这个参数可以指定接收的行为，比较有用的两个选项是：

 这个这次要学习的，它可以接收缓冲区中的数据，但是并不从缓冲区中清除，这是跟read函数有区别的地方，read函数一旦读取了，就会直接从缓冲区中清除。

readline实现

也就是实现按行读取，读取直到 字符，实际上，它也能解决上节中提到的粘包问题，回顾下上节的粘包问题解决方案：

包尾加 (ftp)

我们只要解释 为止，表示前面是一个条合法的消息，对于readline的实现，可以有三种方案：

①、最简单的方案就是一个字符一个字符的读取，然后做判断是否有" "，但是这种效率比较低，因为会多次掉用read或recv系统函数。

②、用一个static变量保存接收到的数据进行缓存，在下次时从这个缓存变量中读取然后估" "判断。但是一旦用到了static变量，这意味着用到的函数是不可重录函数【关于这个概念，可以参考博文：http://www.cnblogs.com/webor2006/p/3744002.html】。

③、偷窥的方法，也就是这次要采用的方案。下面就利用我们封装的recv_peek函数实现readline：

server.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>

#define ERR_EXIT(m)
        do
        {
                perror(m);
                exit(EXIT_FAILURE);
        }while(0);

ssize_t readn(int fd, void *buf, size_t count)//读取count个字节数，其中size_t是无符号
的整数，ssize_t是有符号的整数
{
    size_t nleft = count;//剩余的字节数
    printf("nleft = %d
",nleft);
    ssize_t nread;//已接收的字节数
    char *bufp = (char*)buf;

    while (nleft > 0)
    {//由于不能保证一次读操作能够返回字节数是多少，所以需要进行循环来接收
        if ((nread = read(fd, bufp, nleft)) < 0)
        {
            if (errno == EINTR)//被信号中断了，则继续执行，因为不是出错
                continue;
            return -1;//表示读取失败了
        }
        else if (nread == 0)//对等方关闭了
            return count - nleft;//返回已经读取的字节数

        bufp += nread;
        nleft -= nread;
    } 
          
    return count;
}         
         
ssize_t writen(int fd, const void *buf, size_t count)
{
    size_t nleft = count;
    ssize_t nwritten; 
    char *bufp = (char*)buf;

    while (nleft > 0) 
    {
        if ((nwritten = write(fd, bufp, nleft)) < 0)
        {
            if (errno == EINTR) 
                continue;
            return -1;
        }
        else if (nwritten == 0)//如果是这种情况，则表示什么都没发生，继续还得执行
                continue;

        bufp += nwritten;
        nleft -= nwritten;
    }

    return count;
}

ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
        while(1)
        {
                int ret = recv(sockfd,buf,len,MSG_PEEK);
                if(ret == -1 && errno == EINTR)
                        continue;
                return ret;
        }
}

ssize_t readline(int sockfd, void *buf, size_t maxline)
{
        int ret;
        int nread;
        char *bufp = buf;
        int nleft = maxline;
        while(1)
        {
                ret = recv_peek(sockfd,bufp,nleft);
                if(ret < 0)
                        return ret;
                else if(ret == 0)
                        return ret;
                nread = ret;
                int i;
                for(i = 0; i<nread; i++)
                {
                        if(bufp[i] == '
')
                        {
                                ret = readn(sockfd,bufp,i+1);
                                if(ret != i+1)
                                        exit(EXIT_FAILURE);
                                return ret;
                        }
                }

                if(nread > nleft)
                        exit(EXIT_FAILURE);
                nleft -= nread;
                ret = readn(sockfd,bufp,nread);
                if(ret != nread)
                        exit(EXIT_FAILURE);
                bufp += nread;
        }
        return -1;
}

void do_service(int conn)
{
        char recvbuf[1024];
        //struct packet recvbuf;
        int n;
        while(1)
        {
                memset(recvbuf, 0, sizeof(recvbuf));
                int  ret=readline(conn,recvbuf,1024);
                if(ret == -1)
                {
                        ERR_EXIT("readline");
                }
                if(ret == 0)
                {
                        printf("client close
");
                        break;
                }

                fputs(recvbuf,stdout);
                writen(conn,recvbuf,strlen(recvbuf));
        }
}

int main(void)
{
        int listenfd;
        if((listenfd = socket(PF_INET,SOCK_STREAM,IPPROTO_TCP)) < 0)
        {
                ERR_EXIT("socket");
        }
        struct sockaddr_in servaddr;
        memset(&servaddr, 0, sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        servaddr.sin_port = htons(5188);
        servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
        /*servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");*/
        /*inet_aton("127.0.0.1",&servaddr.sin_addr);*/

        //地址重用
        int on=1;
        if(setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on)) < 0)
        {
                ERR_EXIT("setsockopt");
        }

        if(bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr)) < 0)
        {
                ERR_EXIT("bind");
        }

        if(listen(listenfd,SOMAXCONN) < 0)
        {
            ERR_EXIT("listen");
        }

        struct sockaddr_in peeraddr;
        socklen_t peerlen = sizeof(peeraddr);
        int confd;

        pid_t pid;
        while(1)
        {
                if((confd = accept(listenfd,(struct sockaddr*)&peeraddr, &peerlen)) < 0)
                {
                        ERR_EXIT("accept");
                }
                printf("ip = %s, port = %d
",inet_ntoa(peeraddr.sin_addr),ntohs(peeraddr.sin_port));
                pid = fork();
                if(pid == -1)
                {
                        ERR_EXIT("fork");
                }
                if(pid == 0)
                {
                        close(listenfd);
                        do_service(confd);
                        exit(EXIT_SUCCESS);
                }
                else
                {
                        close(confd);
                }
        }

        return 0;
}

client.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>

#define ERR_EXIT(m)
        do
        {
                perror(m);
                exit(EXIT_FAILURE);
        }while(0);

ssize_t readn(int fd, void *buf, size_t count)//需要将函数的定义也挪过来
{
    size_t nleft = count;
    ssize_t nread;
    char *bufp = (char*)buf;

    while (nleft > 0)
    {
        if ((nread = read(fd, bufp, nleft)) < 0)
        {
            if (errno == EINTR)
                continue;
            return -1;
        }
        else if (nread == 0)
            return count - nleft;

        bufp += nread;
        nleft -= nread;
    }

    return count;
}

ssize_t writen(int fd, const void *buf, size_t count)
{
    size_t nleft = count;
    ssize_t nwritten;
    char *bufp = (char*)buf;

    while (nleft > 0)
    {
        if ((nwritten = write(fd, bufp, nleft)) < 0)
        {
            if (errno == EINTR)
                continue;
            return -1;
        }
        else if (nwritten == 0)
            continue;
        bufp += nwritten;
        nleft -= nwritten;
    }

    return count;
}

ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
        while(1)
        {
                int ret = recv(sockfd,buf,len,MSG_PEEK);
                if(ret == -1 && errno == EINTR)
                        continue;
                return ret;
        }
}

ssize_t readline(int sockfd, void *buf, size_t maxline)
{
        int ret;
        int nread;
        char *bufp = buf;
        int nleft = maxline;
        while(1)
        {
                ret = recv_peek(sockfd,bufp,nleft);
                if(ret < 0)
                        return ret;
                else if(ret == 0)
                        return ret;
                nread = ret;
                int i;
                for(i = 0; i < nread; i++)
                {
                        if(bufp[i] == '
')
                        {
                                ret = readn(sockfd,bufp,i+1);
                                if(ret != i+1)
                                        exit(EXIT_FAILURE);
                                return ret;
                        }
                }

                if(nread > nleft)
                        exit(EXIT_FAILURE);
                nleft -= nread;
                ret = readn(sockfd,bufp,nread);
                if(ret != nread)
                        exit(EXIT_FAILURE);
                bufp += nread;
        }
        return -1;
}

int main(void)
{
        int sockfd;
        if((sockfd = socket(PF_INET,SOCK_STREAM,IPPROTO_TCP)) < 0)
        {
                ERR_EXIT("socket");
        }
        struct sockaddr_in servaddr;
        memset(&servaddr, 0, sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        servaddr.sin_port = htons(5188);
        servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
        /*inet_aton("127.0.0.1",&servaddr.sin_addr);*/

        if (connect(sockfd,(struct sockaddr*)&servaddr,sizeof(servaddr)) < 0)
        {
                ERR_EXIT("connect");
        }

        struct sockaddr_in localaddr;
        socklen_t addrlen = sizeof(localaddr);
        if(getsockname(sockfd,(struct sockaddr*)&localaddr,&addrlen) < 0)
                ERR_EXIT("getsockname");
        printf("ip = %s, port = %d
",inet_ntoa(localaddr.sin_addr),ntohs(localaddr.s
in_port));

        char sendbuf[1024] = {0};
        char recvbuf[1024] = {0};
        //struct packet sendbuf;
        //struct packet recvbuf;
        //memset(&sendbuf,0,sizeof(sendbuf));
        //memset(&recvbuf,0,sizeof(recvbuf));

        int n;

        while(fgets(sendbuf,sizeof(sendbuf),stdin) != NULL)
        {
                //writen(sockfd,sendbuf,sizeof(sendbuf));
                //readn(sockfd,recvbuf,sizeof(recvbuf));
                //n =strlen(sendbuf.buf);
                //sendbuf.len = htonl(n);//网络字节序
                writen(sockfd,sendbuf,strlen(sendbuf));
                int ret = readline(sockfd,recvbuf,sizeof(recvbuf));
                //int ret = readn(sockfd,&recvbuf.len,4);
                if(ret == -1)
                {
                        ERR_EXIT("read");
                }
                else if(ret == 0)
                {
                        printf("client close
");
                        break;
                }

                fputs(recvbuf,stdout);
                memset(sendbuf,0,sizeof(sendbuf));
                memset(recvbuf,0,sizeof(recvbuf));
        }
        close(sockfd);
        return 0;
}

Makefile

.PHONY: clean all
CC=gcc
CFLAGE= -G -Wall
BIN=client server getiplist
all:$(BIN)
%.o:%.c
        $(CC) $(cflags) -C $< -O $@
clean:
        rm -f *.o $(BIN)

getsockname:获取套接口本地的地址

当客户端成功与服务端连接之后，如果想知道客户端的地址，就可以通过它来获取，

getpeername:获取对等方的地址

由于它的使用方法跟getsockname一样，这里就不说明了，注意：sockfd需是连接成功的套接口，另外对于服务端获取客户端ip，像这种情况下也需用这个接口来获得：

 gethostname:获取主机的名称

gethostbyname:通过主机名来获取主机上所有的ip地址

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

#define ERR_EXIT(m) 
        do 
        { 
                perror(m); 
                exit(EXIT_FAILURE); 
        } while(0)

int getlocalip(char *ip)
{
    char host[100] = {0};
    if (gethostname(host, sizeof(host)) < 0)
      return -1;
    struct hostent *hp;
    if ((hp = gethostbyname(host)) == NULL)
      return -1;
    strcpy(ip, inet_ntoa(*(struct in_addr*)hp->h_addr_list[0]));
    return 0;

}

int main(void)
{
    char host[100] = {0};
    if (gethostname(host, sizeof(host)) < 0)
        ERR_EXIT("gethostname");

    struct hostent *hp;
    if ((hp = gethostbyname(host)) == NULL)
        ERR_EXIT("gethostbyname");

    int i = 0;
    while (hp->h_addr_list[i] != NULL)
    {
        printf("%s
", inet_ntoa(*(struct in_addr*)hp->h_addr_list[i]));
        i++;
    }

    char ip[16] = {0};
    getlocalip(ip);
    printf("localip=%s
", ip);
    return 0;
}
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原文地址：https://www.cnblogs.com/Malphite/p/11645067.html