strstr issue

Using Arduino Programming Questions
#1

Hello,

I am getting desperate with the string functions.
I receive from a device the following string “00 FF 00 01 2C” in HEX (<\0>ÿ<\0><1>,) in ASCII.
I have to react to this message.
If, for testing, I only receive 01 2C, it is recognised. But the complete line is not.
The character string that I receive cannot be changed because it is fixed in the firmware.

Here is the programme part:

int counter = 0;
char linebuf[30];
char finden[] = {0x00, 0xFF, 0x00, 0x01, 0x2C};
//char finden[] = {0x01, 0x2C};

  if (Serial.available()) {//2
    delay(10); // Warte auf das Eintreffen aller Zeichen vom seriellen Monitor
    memset(linebuf, 0, sizeof(linebuf)); // Zeilenpuffer löschen
    counter = 0; // Zähler auf Null
    while (Serial.available()) {//3
      linebuf[counter] = Serial.read(); // Zeichen in den Zeilenpuffer einfügen
      if (counter < sizeof(linebuf) - 1) counter++; // Zeichenzähler erhöhen
    }//3
    
    //Test          00 FF 00 01 2C
    if (strstr(linebuf, finden) == linebuf) {
        Serial.print("gefunden");
    }else{
      Serial.print("nicht gefunden");
    }
    //Test
}

In the “linebuf”, other commands are searched for, which works without any problems because only ASCII characters greater than 30 occur there.

I assume that if “strstr” reads 0x00, it doesn’t work.

What can I do there?

#2

you could make your own strstr.

something like this maybe…

int  my_strstr(const char *haystack, int haystack_len, const char *needle, int needle_len)
{
  int i = 0;
  while (i < haystack_len)
  {
    if (haystack[i] == *needle)
    {
      if (!strncmp(haystack + i, needle, needle_len))
        return i;
    }
    i++;
  }
  return -1;
}

void setup() {
  Serial.begin(115200);

  int counter = 0;
  char linebuf[30];
  char finden_1[] = {0x00, 0xFF, 0x00, 0x01, 0x2C};
  char finden[] = {0x01, 0x2C};

  //Test          00 FF 00 01 2C
  Serial.println(my_strstr(finden_1, 5, finden, 2)); // returns the position on 'finden' in finden_1
  //Test
}

void loop() {

}

the other option is to check each element of the received array for a match.
hope that helps

#3

Hello
Thanks for the answer.
I have managed it with “memcmp”.
Here I compare the 2 memory areas directly. So the content doesn’t matter. It only has to match.

int pos = memcmp ( linebuf, finden, sizeof(finden) );

    if (pos == 0) {//3
      startStringComplete = true;
      Serial.print("gefunden");
    }else{
      Serial.print("Fehler!");  //Fehler bei pos<0; pos>0
    }
#4

You cannot use strstr to test for a sequence of characters that contain nulls (0x00) because the null indicates the end of the char array you are passing to the strstr function.

I receive from a device the following string “00 FF 00 01 2C” in HEX (<\0>ÿ<\0><1>,) in ASCII.

That does not make sense - from your code it appears the received data is in binary, not ASCII. “00” in ASCII is 0x30 0x30, not 0x00 as you have in the finden array.

#5