UDP通信的实现过程

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

sendto与recvfrom

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；

实现代码

server.c

#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;
}

client.c

#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 编译文件

CC = gcc
CFLAGS = -Wall 

all: server client

server: server.c
	$(CC) $(CFLAGS) -o server server.c

client: client.c
	$(CC) $(CFLAGS) -o client client.c

clean:
	rm -f server client