linux 基于UDP，实现tftp上传文件（客户端）

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#define RRQ   1
#define WRQ   2
#define DATA  3 
#define ACK   4
#define ERROR 5



int main(int argc, char **argv){

//检测命令行3个参数
    if (3 != argc)
    {
        printf("please use :%s   <ip>  <port>\n",argv[0]);
        exit(-1);
    }
    
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (-1 == sockfd)
        perror("socket");

	struct sockaddr_in server_addr;
	memset(&server_addr, 0, sizeof(server_addr)); 
	server_addr.sin_family = AF_INET; // IPV4
	server_addr.sin_port = htons(atoi(argv[2]));
	server_addr.sin_addr.s_addr = inet_addr(argv[1]);
	socklen_t server_addr_len = sizeof(ser