recvmsg()和sendmsg()函数(2)

转自：http://memorymyann.iteye.com/blog/648513

想对于之前的几个IO函数，recvmsg与sendmsg功能更为强大，当然用起来也更为复杂。

#include "sys/socket.h"

ssize_t recvmsg(int sockfd,  struct msghdr * msg, int flags);

ssize_t sendmsg(int sockfd,  struct msghdr * msg, int flags);

成功时候返回读写字节数，出错时候返回-1.

 

这2个函数只用于套接口，不能用于普通的I/O读写，参数sockfd则是指明要读写的套接口。

flags用于传入控制信息，一般包括以下几个

MSG_DONTROUTE             send可用

MSG_DONWAIT                 send与recv都可用

MSG_PEEK                        recv可用

MSG_WAITALL                   recv可用

MSG_OOB                         send可用

MSG_EOR                          send recv可用

 

返回信息都记录在struct msghdr * msg中。

struct msghdr {       void * msg_name;//协议地址和套接口信息，在非连接的UDP中，发送者要指定对方地址端口，接受方用于的到数据来源，如果不需要的话可以设置为NULL（在TCP或者连接的UDP中，一般设置为NULL）。        socklen_t msg_namelen;//上面的长度        struct lovec * msg_lov;        ssize_t msg_lovlen;//和readv和writev一样        void * msg_control;        socklen_t msg_controllen;        int msg_flags; //用于返回之前flags的控制信息}

样例1，在TCP中使用 sendmsg与recvmsg

 

服务器

......

#define MAXSIZE 100int main(int argc, char ** argu) {        .......        struct msghdr msg;//初始化struct msghdr        msg.msg_name = NULL; //在tcp中，可以设置为NULL        struct iovec io;//初始化返回数据        io.iov_base = buf; //只用了一个缓冲区        io.iov_len = MAXSIZE; //定义返回数据长度        msg.msg_iov = &io;        msg.msg_iovlen = 1;//只用了一个缓冲区，所以长度为1        ...................        ssize_t recv_size = recvmsg(connfd, &msg, 0);        char * temp = msg.msg_iov[0].iov_base;//获取得到的数据        temp[recv_size] = '\0';//为数据末尾添加结束符        printf("get message:%s", temp);        ..........................}

客户端

..................

#define MAXSIZE 100int main(int argc, char ** argv) {        .................        struct msghdr msg;//初始化发送信息        msg.msg_name = NULL;        struct iovec io;        io.iov_base = send_buff;        io.iov_len = sizeof(send_buff);        msg.msg_iov = &io;        msg.msg_iovlen = 1;        if(argc != 2) {                printf("please input port");                exit(1);        }        ............        ssize_t size = sendmsg(sockfd, &msg, 0);        close(sockfd);        exit(0);}

这里控制信息都设置成0，主要是初始化返回信息struct msghdr结构。关于struct iovec这个数据结构，上一篇readv与writev有介绍。

未连接的UDP套接口

服务器#include "/programe/net/head.h"#include "stdio.h"#include "stdlib.h"#include "string.h"#include "unistd.h"#include "sys/wait.h"#include "sys/select.h"#include "sys/poll.h"#define MAXSIZE 100int main(int argc, char ** argv) {        int sockfd;        struct sockaddr_in serv_socket;        struct sockaddr_in  * client_socket = (struct sockaddr_in *) malloc (sizeof(struct sockaddr_in));        char buf[MAXSIZE + 1];        sockfd = socket(AF_INET, SOCK_DGRAM, 0);        bzero(&serv_socket, sizeof(serv_socket));        serv_socket.sin_family = AF_INET;        serv_socket.sin_addr.s_addr = htonl(INADDR_ANY);        serv_socket.sin_port = htons(atoi(argv[1]));        bind(sockfd, (struct sockaddr *)&serv_socket, sizeof(serv_socket));        struct msghdr msg;        msg.msg_name = client_socket;        //如果想得到对方的地址和端口，一定要把初始化完毕的内存头指针放入msg之中        msg.msg_namelen = sizeof(struct sockaddr_in);//长度也要指定        struct iovec io;        io.iov_base = buf;        io.iov_len = MAXSIZE;        msg.msg_iov = &io;        msg.msg_iovlen = 1;        ssize_t len = recvmsg(sockfd, &msg, 0);        client_socket = (struct sockaddr_in *)msg.msg_name;        char ip[16];        inet_ntop(AF_INET, &(client_socket->sin_addr), ip, sizeof(ip));        int port = ntohs(client_socket->sin_port);        char * temp = msg.msg_iov[0].iov_base;        temp[len] = '\0';        printf("get message from %s[%d]: %s\n", ip, port, temp);        close(sockfd);}

客户端#include "/programe/net/head.h"#include "stdio.h"#include "stdlib.h"#include "string.h"#include "sys/select.h"#define MAXSIZE 100int main(int argc, char ** argv) {        int sockfd;        struct sockaddr_in serv_socket;        int maxfdpl;        char send[] = "hello yuna";        if(argc != 2) {                printf("please input port");                exit(1);        }        sockfd = socket(AF_INET, SOCK_DGRAM, 0);        bzero(&serv_socket, sizeof(serv_socket));        serv_socket.sin_family = AF_INET;        serv_socket.sin_port = htons(atoi(argv[1]));        inet_pton(AF_INET, "192.168.1.235", &serv_socket.sin_addr);        struct msghdr msg;        msg.msg_name = &serv_socket;        msg.msg_namelen = sizeof(struct sockaddr_in);        struct iovec io;        io.iov_base = send;        io.iov_len = sizeof(send);        msg.msg_iov = &io;        msg.msg_iovlen = 1;        ssize_t send_size = sendmsg(sockfd, &msg, 0);        close(sockfd);        exit(0);}