Weird characters after device read

Hi all. I am writing a simple program that reads from the serial port. I have got the communications working file, but get weird characters after using the read command such as below:

׵sӵ������׹���������

Any ideas what might cause this? I am not that familiar with C (from java background) and to me this looks like I should read this input stream as something else than character array. However from all documentation I have seen for the read function, it always reads the data to character array.

Any pointers anyone?

Regards,

Olli

Do yo you get actual data prior to that? If so you need to null terminate the buffer after you've read it in order to treat it as a string.

pseudocode:

Code:

---

bytesread=read into buffer
if bytesread > 0
    buffer[bytesread] = 0
    print buffer

---

My code is as below:

Code:

---

char data[160];
int readbytes;

readbytes = read(fd,data,160);
while(readbytes>0)
{
  cout << data << "\n";
  readbytes = read(fd,data,160);
}

---

I modified this to:

Code:

---

readbytes = read(fd,data,160);
while(readbytes>0)
{
  data[readbytes]= '\0';
  cout << data << "\n";
  readbytes = read(fd,data,160);
}

---

But still the same result.

What operating system are you using? Also insure the sending and receiving serial ports are configured for the same settings. Does your incoming data have any sort of delimiter? ie( '\r' or '\n'). Also you might want to print the character array char by char converting to int.

Code:

---

  for(int i = 0; i < data.length(); ++i)
      printf("%d ",data[i]);

---

You might then be able to determine what is going on.

Yeah it should return something like this:

Plugwise protocol unleashed part 1: introduction | Maartendamen's blog

So the data has "\r\n\0" as terminator. If I convert all characters to int one by one I seem to get range of negative values.

If you get negative values back, presumably that means that all your data has the high bit set (extended ASCII, or characters > 128). (EDIT: Of course, hopefully that's what you want, otherwise you'll have to figure out how your device is sending the data.) (ANOTHER EDIT: If you want to post the first few, maybe someone will be able to recognize the characters, or see some pattern in what you're getting.)

> readbytes = read(fd,data,160);
160 is a maximum limit, not a demand.

Unless you're reading from a fast device like a disk, chances are the OS will return whenever there is SOME data to be read.

This typically means your buffer will only be partly filled.
Also, few low level routines explicitly add a \0 to the end of the buffer for you (so you can't immediately treat the result as a proper C-string).

Try

Code:

---

while ( (readbytes = read(fd,data,160)) > 0 ) {
  for ( i = 0 ; i < readBytes ; i++ ) {
    printf("%c", data[i] );  // if you're sure all the data is printable, otherwise use say %d or %x
  }
}

---

thank you all for your input.

It seems like I get a different result back everytime(when converting characters to d or x), so starting to think that either there is something wrong with the device or maybe the way I write first to it in order to make it to respond.

You may have to cast your char to an int in the printf

Code:

---

  printf("%d ", int(data[i]));

---

Figured it out in the end. Was passing the port the wrong tty settings by accident, hence the bad character encoding.

Nice job, and thanks for the update :)