Problems with pointers and strstr()...

Projects Programming
1

Hello,
I am trying to extract part of text in an array of char.
Below, I try to extract : "123.145.789.123", but the second step already does not work.
I am also confused between pointers, arrays, etc.
If anyone wants to explain to me, I'm interested.
Thank you.

  char t1[50];
  char t2[10];
  char* t3;

  snprintf(t1, sizeof(t1), "+CDNSGIP: 1,\"www.truc.com\",\"123.145.789.123\"");
  snprintf(t2, sizeof(t2), ",");
  t3 = strstr(t1, t2);
  Serial.print(t3);            // j'obtiens biens : ,"www.truc.com","123.145.789.123"
  t3 = strstr(t3, t2);
  Serial.println(t3);          // j'obtiens toujours : ,"www.truc.com","123.145.789.123"
2

What does "Does Not Work" mean?

How does the code as written behave?

How do you want it to behave differently?

3

Hi gfvalvo,

Thanks for your reply.

The first step works correctly regarding strstr() :

snprintf(t1, sizeof(t1), "+CDNSGIP: 1,\"www.truc.com\",\"123.145.789.123\"");
  snprintf(t2, sizeof(t2), ",");
  t3 = strstr(t1, t2);
  Serial.print(t3);            // I get : ,"www.truc.com","123.145.789.123"

But if continue with strstr() on t3, I expect to get : ,"123.145.789.123".

t3 = strstr(t3, t2);
  Serial.println(t3);          // I still get : ,"www.truc.com","123.145.789.123" and not ,"123.145.789.123"

But I get the same return as the first step : ,"www.truc.com","123.145.789.123"...

What I want is to extract only the IP address.

Thanks

4

You will have to increment t3 before the second step. After the first step, that first char is a comma. Next you use strstr and what will it find? The first character.

 t3 = strstr(t1, t2);
  Serial.print(t3);            // j'obtiens biens : ,"www.truc.com","123.145.789.123"

  // increment t3 so it points to the next character
  t3++;
  t3 = strstr(t3, t2);
  Serial.println(t3);

If you're only looking for a single character, use strchr(). E.g.

 t3 = strchr(t1, ',');
  Serial.print(t3);            // j'obtiens biens : ,"www.truc.com","123.145.789.123"

  // increment t3 so it points to the net character
  t3++;
  t3 = strchr(t3, ',');
  Serial.println(t3);

There is also the function strtok() which is usually used for parsing; it however is destructive in the sense that it destroys the input string.

// Note
t3++ increments the pointer, not the character that it points at.

5

For the second call to strstr(), try:

t3 = strstr(t3+1, t2);

Untested.

6

Thanks gfvalvo, sterretje,

It works perfectly now !

Bruno.