Serial Port Programming in Linux

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <termios.h>
#include <stdlib.h>
#include <unistd.h> 
#include <time.h>

int main(){
	FILE *fd;
	struct termios options;

	fd = open("/dev/ttyUSB0",O_RDWR | O_NOCTTY);
	if(fd){
		//fcntl(fd,F_SETFL,0);
		printf("port opening successful %d .file description is\n",fd);
	}else{
		perror("Open port failded");
	}

	//serial configure
	/*tcgetattr(fd,&options);	

	cfsetispeed(&options,B9600);
	cfsetospeed(&options,B9600);
	options.c_cflag &= _CSIZE;
	options.c_cflag &= _CS8;
	options.c_cflag &= _PARENB; */

	int rr,r,w;
	char buf[255];

	printf("Writing\r\n");
	w = write(fd,"AT\n",16);
	printf("unsleeping\r\n");
	usleep(100000);
	printf("Reading\r\n");
	r=read(fd,buf,6);
	printf("Read\r\n");
	if(r>0){
		printf("Data: %s \r\n",buf);
	}
	close(fd);
	printf("Hello world \n");
	return 0;
}</time.h></unistd.h></stdlib.h></termios.h></fcntl.h></string.h></stdio.h>