个体户营业执照在线办理/厦门seo搜索排名

一、函数接口扩展与UDP通信实现流程

1.write/read到send/recv

函数原型：

        ssize_t send(int sockfd, const void *buf, size_t len, int flags);

        ssize_t recv(int sockfd, void *buf, size_t len, int flags);

前三个参数同read/write一样；

         ssize_t read(int fd, void *buf, size_t count);

        ssize_t write(int fd, const void *buf, size_t count);

常见flags:

        1. 一般设置为0

        2. MSG_PEEK：窥视传入的数据。数据被复制到缓冲区中，但不会从输入队列中删除。

         3. MSG_OOB：处理带外（OOB）数据

2.sendto与recvfrom

函数原型：

        ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen);

        ssize_t sendto(int sockfd, const void *buf, size_t len, int flags, const struct sockaddr *dest_addr, socklen_t addrlen);

1. 前四个参数同recv/send一样；

2. 后两个参数是通信结构体和结构体的宽度； 

3.UDP通信的实现过程

二、UDP服务器代码 

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <strings.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>int main(int argc, char *argv[])
{int fd;struct sockaddr_in addr;char buf[BUFSIZ] = {};if(argc < 3){fprintf(stderr, "%s<addr><port>\n", argv[0]);exit(EXIT_FAILURE);}/*创建套接字*/if( (fd = socket(AF_INET, SOCK_DGRAM, 0) ) < 0){perror("socket");exit(EXIT_FAILURE);}/*设置通信结构体*/bzero(&addr, sizeof(addr) );addr.sin_port = htons( atoi(argv[2]) );if(inet_aton(argv[1], &addr.sin_addr) == 0) {fprintf(stderr, "Invalid address\n");exit(EXIT_FAILURE);}/*绑定通信结构体*/if(bind(fd, (struct sockaddr *)&addr, sizeof(addr) ) == -1){perror("bind");exit(EXIT_FAILURE);}while(1){bzero(buf, BUFSIZ);recvfrom(fd, buf, BUFSIZ, 0, NULL, NULL);printf("buf=%s\n", buf);}close(fd);return 0;
}

三、客户端

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <strings.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>int main(int argc, char *argv[])
{int fd;struct sockaddr_in addr;char buf[BUFSIZ] = {};socklen_t addrlen = sizeof(addr);if(argc < 3){fprintf(stderr, "%s<addr><port>\n", argv[0]);exit(EXIT_FAILURE);}/*创建套接字*/if( (fd = socket(AF_INET, SOCK_DGRAM, 0) ) < 0){perror("socket");exit(EXIT_FAILURE);}/*设置通信结构体*/bzero(&addr, sizeof(addr) );addr.sin_port = htons( atoi(argv[2]) );if(inet_aton(argv[1], &addr.sin_addr) == 0) {fprintf(stderr, "Invalid address\n");exit(EXIT_FAILURE);}while(1){bzero(buf, BUFSIZ);printf("Input->");fgets(buf, BUFSIZ, stdin);sendto(fd, buf, strlen(buf), 0, (struct sockaddr *)&addr, addrlen);}close(fd);return 0;
}

Makefile

CC=gcc
CFLAGS=-Wall
all:server client

clean:
    rm server client