可用数据时从串行端口读取

Question

I'm trying to write a program that communicates with serial port which is connected to GSM modem. Using AT command to communicate with modem. Here's my code. Got it from http://tldp.org/HOWTO/Serial-Programming-HOWTO/x115.html - Canonical Input Processing.

It works fine when output returns single line. For example:

AT returns OK

And my problem is If i send AT+CPIN? which returns several lines for example:
+CPIN: SIM PIN
OK

but my program reads only +CPIN: SIM PIN and breaks.How to fix it ?

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

#define BAUDRATE B38400            
#define dev "/dev/ttyUSB0"
#define _POSIX_SOURCE 1

#define FALSE 0
#define TRUE 1

volatile int STOP=FALSE; 

main()
{
  char pinn[20];
  char buf[255];
  int fd,res=0;
  printf("%s\n", dev);
  struct termios oldtio,newtio;
  fd = open(dev, O_RDWR | O_NOCTTY ); 
  if (fd <0) {perror(dev); exit(-1); }
  bzero(&newtio, sizeof(newtio));
  newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
  newtio.c_iflag = IGNPAR | ICRNL;
  newtio.c_oflag = 0;
  newtio.c_lflag = ICANON;
  newtio.c_cc[VMIN]     = 1;
  tcflush(fd, TCIFLUSH);
  tcsetattr(fd,TCSANOW,&newtio);


  if (fd < 0)
  {
      printf("Error opening serial port\n");
      exit(1);
  }
  while(1){

    scanf("%s",pinn);
    strcat(pinn,"\r");

    if (write(fd, pinn, strlen(pinn)) < strlen(pinn)) printf("Write error - %s \n", strerror(errno));
    pinn[strlen(pinn)-1]=0;
    while(1){
      res = read(fd,buf,255);
      buf[res]=0;
      buf[res-1]=0;
      if (res>1&&NULL==strstr(buf,pinn)) break;
    }
    printf("\"%s\"\n", buf);
  }
  close(fd);
}

code UPDATE removed duplicate read

Answer 1

Besides other minor deficiencies of the code, your receiving while() loop will terminate if the returned string does not contain the command you initially sent (NULL==strstr(buff, pinn)) .

This condition is obviously not met when you receive multiline results (as only the first line contains the AT command you sent).

You need to change that if you don't want it.