实现uclinux下网络通信（UDP）

目标：实现uclinux下网络通信（UDP），采用c/s模式，客户端发送预定义的字符串，以及发送由键盘输入的字符串，服务器收到字符串口，回送相同的字符串给客户端，并通过串口显示在屏幕上。

遇见过的问题：
1.一直无法打开sock
2.客户端发送成功，服务器端接收错误

相关代码如下：（参考嵌入式linux应用开发详解，源程序存在错误，做适当修改后调试成功）

/*服务端程序UDPServer.c*/
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <errno.h>
#define SERVER_PORT     8000
#define MAX_MSG_SIZE    100

void udps_respon(int sockfd)
{
        struct sockaddr_in addr;
        int     addrlen,n;
        char    msg[MAX_MSG_SIZE];
       
  while(1)
        {       /*等待数据请求*/
  //printf("test point 2."n");
                n=recvfrom(sockfd,msg,MAX_MSG_SIZE,0,(struct sockaddr*)&addr,&addrlen);
  //printf("test point 3 %d."n",n);
                msg[n]=0;

    if (n==-1)
    {
     printf("fail receive from the client."n");
     exit(1);
    }

                /*显示服务器端已经收到了信息*/
                fprintf(stdout,"I have received %s",msg);
    /*数据回送*/
                sendto(sockfd,msg,n,0,(struct sockaddr*)&addr,addrlen);
        }
}

int main(void)
{
        int sockfd;
        struct sockaddr_in      addr;
       
        sockfd=socket(AF_INET,SOCK_DGRAM,0);
        if(sockfd<0)
        {
                fprintf(stderr,"Socket Error:%s"n",strerror(errno));
                exit(1);
        }
        bzero(&addr,sizeof(struct sockaddr_in));
        addr.sin_family=AF_INET;
        addr.sin_addr.s_addr=htonl(INADDR_ANY);
        addr.sin_port=htons(SERVER_PORT);
        if(bind(sockfd,(struct sockaddr *)&addr,sizeof(struct sockaddr))<0)
        {
                fprintf(stderr,"Bind Error:%s"n",strerror(errno));
                exit(1);
        }
  printf("test point 1."n");                   //注意，这里的打印语句引掉的话，就会出现错误，原因不明
        udps_respon(sockfd);
        close(sockfd);
}

/*客户端程序UDPClient.c，使用方法UDPClient ServerIP ServerPort*/
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#define MAX_BUF_SIZE    100

void udpc_requ(int sockfd,const struct sockaddr_in *addr,int len,int port)
{
        char buffer[MAX_BUF_SIZE];
        int n,numto,addrlen;
  char how[]="successed in sending data form subfunction!"n";
  struct sockaddr_in new_addr;

  addrlen=len;
        bzero(&new_addr,sizeof(struct sockaddr_in));
        new_addr.sin_family=AF_INET;
        new_addr.sin_port=htons(port);

  if(inet_aton("192.168.1.100",&new_addr.sin_addr)<0)
        {
                fprintf(stderr,"Ip error:%s"n",strerror(errno));
                exit(1);
        }

 

        while(1)       
        {        /*从键盘读入，写到服务端*/
                fgets(buffer,MAX_BUF_SIZE,stdin);
    //fprintf(stdout,"the input text are:%s",buffer);

                numto = sendto(sockfd,buffer,strlen(buffer),0,(struct sockaddr*)&new_addr,sizeof(struct sockaddr));
    if (numto==-1)
    {
     printf("send failed."n");
    }

                bzero(buffer,MAX_BUF_SIZE);
                /*从网络上读，写到屏幕上*/
                n=recvfrom(sockfd,buffer,MAX_BUF_SIZE,0,NULL,NULL);
                buffer[n]=0;
                fputs(buffer,stdout);
        }
}

int main(int argc,char **argv)
{
        int sockfd,port,num,rnum;
        struct sockaddr_in      addr;
  char rebuffer[MAX_BUF_SIZE];
  char hello[]="hello,socket communication world."n";
   
        if(argc!=3)
        {
                fprintf(stderr,"Usage:%s server_ip server_port"n",argv[0]);
                exit(1);
        }
       
        if((port=atoi(argv[2]))<0)
        {
                fprintf(stderr,"Usage:%s server_ip server_port"n",argv[0]);
                exit(1);
        }
       
        sockfd=socket(AF_INET,SOCK_DGRAM,0);
        if(sockfd<0)
        {
                fprintf(stderr,"Socket  Error:%s"n",strerror(errno));
                exit(1);
        }      
        /*填充服务器端的资料*/
        bzero(&addr,sizeof(struct sockaddr_in));
        addr.sin_family=AF_INET;
        addr.sin_port=htons(port);
        if(inet_aton(argv[1],&addr.sin_addr)<0)
        {
                fprintf(stderr,"Ip error:%s"n",strerror(errno));
                exit(1);
        }

                num=sendto(sockfd,hello,strlen(hello),0,(struct sockaddr*)&addr,sizeof(struct sockaddr));
    if (num==-1)
    {
     printf("send failed."n");
    }
    //printf("send %d data to server/"n",num);

    rnum=recvfrom(sockfd,rebuffer,MAX_BUF_SIZE,0,NULL,NULL);
    if (rnum==-1)
    {
     printf("send failed."n");
    }
    //printf("received %d data from server/"n",rnum);
                rebuffer[rnum]=0;
                fputs(rebuffer,stdout);

        udpc_requ(sockfd,&addr,sizeof(struct sockaddr_in),port);
        close(sockfd);
}

总结：
1.在linux下分别对服务器端，客户端程序编译成功，实现在linux下通信成功。
2.在linux下用arm-gcc编译成目标板上能运行得二进制文件，通过wftp下载到目标板后成功实现预定功能。编译命令：arm-elf-gcc -Wall -O2 -elf2flt -o 文件名（无后缀） 文件名（带后缀.c）