Programming

/* terminal flags are set in above part of code*/
        tty_fd=open(argv[1], O_RDWR | O_NONBLOCK);//argv[1] is /dev/modem
          unsigned char buff_in[255];
        unsigned char buff_out[255];
        memset(buff_out,'\0',sizeof(buff_out))        sprintf(buff_in,"AT\r");
         int m = write(tty_fd,buff_in,strlen(buff_in));
           memset(buff_out,'\0',sizeof(buff_out));
         if (read(tty_fd,&buff_out,2)>0)
         {
                 printf("\nRead from tty_fd sucess");
                 if(strncmp(buff_out,"OK",2)==0)
                 {
                         printf("\nConnection with Modem works Fine");
                 }else
                 {
                         printf("\nError in connection with modem");
                         return 0;
                 }
         }
         memset(buff_in,'\0',sizeof(buff_in));
         sprintf(buff_in,"AT+CMSS=1\r");
         write(tty_fd,&buff_in,sizeof(buff_in));
         memset(buff_out,'\0',sizeof(buff_out));
         if (read(tty_fd,&buff_out,2)>0)
         {
                 if(strcmp(buff_out,"OK")==0)
                 {
                         printf("\nSIM supports SMS services");
                 }else
                 {
                         printf("\nSIM do not supports SMS services");
                         return 0;
                 }
         }
         memset(buff_in,'\0',sizeof(buff_in));
         sprintf(buff_in,"AT+CMGS=\"+91xxxxxxxx\"\r");
        write(tty_fd,buff_in,strlen(buff_in));
        sleep(5);
        memset(buff_in,'\0',sizeof(buff_in));
         sprintf(buff_in,"Hello SMS Test\r\x1A\r");
        write(tty_fd,buff_in,strlen(buff_in));                      
        memset(buff_out,'\0',sizeof(buff_out));
         if (read(tty_fd,&buff_out,35)>0)
         {
                 int value = buff_out[7];
                 printf("\n Value of buff_out[7] is :- %d",value);
                 if(value <0 || value >255)
                 {
                         printf("\nError in sending msg");
                         return 0;
                 }else
                 {
                         printf("\nMsg sent Sucessfully");
                 }
         }          close(tty_fd);
         return 0;
 }

int main(int argc,char** argv)
{
        struct termios tio;
        struct termios stdio;
        int tty_fd;
        fd_set rdset;
        unsigned char c='D';
        printf("Please start with %s /dev/ttyS1 (for example)\n",argv[0]);
        memset(&stdio,0,sizeof(stdio));
        stdio.c_iflag=0;
        stdio.c_oflag=0;
        stdio.c_cflag=0;
        stdio.c_lflag=0;
        stdio.c_cc[VMIN]=1;
        stdio.c_cc[VTIME]=0;
        tcsetattr(STDOUT_FILENO,TCSANOW,&stdio);
        tcsetattr(STDOUT_FILENO,TCSAFLUSH,&stdio);
        fcntl(STDIN_FILENO, F_SETFL, O_NONBLOCK);       // make the reads non-blocking
 

        memset(&tio,0,sizeof(tio));
        tio.c_iflag=0;
        tio.c_oflag=0;
        tio.c_cflag=CS8|CREAD|CLOCAL;           // 8n1, see termios.h for more information
        tio.c_lflag=0;
        tio.c_cc[VMIN]=1;
        tio.c_cc[VTIME]=5;
        tty_fd=open(argv[1], O_RDWR | O_NONBLOCK);
        cfsetospeed(&tio,B115200);            // 115200 baud
        cfsetispeed(&tio,B115200);            // 115200 baud
        tcsetattr(tty_fd,TCSANOW,&tio);
        while (c!='q')
        {
                if (read(tty_fd,&c,1)>0)        write(STDOUT_FILENO,&c,1);              // if new data is available on the serial port, print it out
                if (read(STDIN_FILENO,&c,1)>0)  write(tty_fd,&c,1);                     // if new data is available on the console, send it to the serial port
        }
        close(tty_fd);
}