udp_echo_cli.c

linux下的多个网络通讯的例子 可多参考下

#include <stdio.h>                                                                
#include <stdlib.h>                                                               
#include <errno.h>                                                                
#include <string.h>                                                               
#include <sys/types.h>                                                            
#include <netinet/in.h>                                                           
#include <netdb.h>                                                                
#include <sys/socket.h>                                                           
#include <sys/wait.h>                                                             
                                                                                  
#define MYPORT 4950    /* the port users will be sending to */                    
                                                                                  
int main(int argc, char *argv[])                                                  
{                                                                                 
    int sockfd;                                                                   
    struct sockaddr_in their_addr; /* connector's address information */          
    struct hostent *he;                                                           
    int numbytes,addr_len;  
    char buffer[512];                                                               
                                                                                  
    if (argc != 3) {                                                              
        fprintf(stderr,"usage: talker hostname message\n");                       
        exit(1);                                                                  
    }                                                                             
    
    /* 尝试做一下域名转换*/                                                                                
    if ((he=gethostbyname(argv[1])) == NULL) {  /* get the host info */           
        perror("gethostbyname");                                                  
        exit(1);                                                                  
    }                                                                             
    
    /* 第一步：打开一个UDP socket ,AF_INET指IPV4,SOCK_DGRAM表示是UDP*/                                                                               
    if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {                        
        perror("socket");                                                         
        exit(1);                                                                  
    }  
    
    /*注意这里没有使用BIND,这样协议栈将随机取一个端口作为本地Socket端口*/                                                                           
    
    /* 第二步：设置服务器的IP和端口*/                                                                               
    their_addr.sin_family = AF_INET;      /* host byte order */                   
    their_addr.sin_port = htons(MYPORT);  /* short, network byte order */         
    their_addr.sin_addr = *((struct in_addr *)he->h_addr);                        
   // bzero(&(their_addr.sin_zero), 8);     /* zero the rest of the struct */ 
   memset(&(my_addr.sin_zero),0,8);      
        
    /* 向服务器发送一个字符串*/  
                                                                               
    if ((numbytes=sendto(sockfd, argv[2], strlen(argv[2]), 0, (struct sockaddr *)&their_addr, sizeof(struct sockaddr))) == -1) {       
        perror("sendto");                                                         
        exit(1);                                                                  
    }                                                                             
                                                                                  
    printf("-sent %d bytes to %s\n",numbytes,inet_ntoa(their_addr.sin_addr));   
    
    /* 等待接收服务器的ECHO字符串 */    
    if ((numbytes=recvfrom(sockfd, buffer, sizeof(buffer), 0, (struct sockaddr *)&their_addr, &addr_len)) == -1) {       
		        perror("recvfrom");                                                       
		        exit(1);                                                                  
		    }   
		    
		 printf("recv %d string:%s\n",numbytes,buffer);     
     
    /* 关闭SOCKET*/                                                                              
    close(sockfd);                                                                
                                                                                  
    return 0;                                                                     
}