Substring of a char* in arduino

Projects Programming
1

Following is a part of the code

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");

Now, I want to compare on a small part of the TOPIC in the function callback.

I tried

topic.substring(14,27) == "certain string"

But it gives an error. Obviously because I am trying to SUBSTRING a *CHAR type.

How can I do the comparison of only a small part of the string in this case with the least memory use?

2

I get an error too.

How can anyone do a comparison of only a small part of your code in this case with the least information?

3

strstr() maybe, but we really need more information.

4

OK.
when I print the topic with
Serial.print(topic)

The output I get is

abc/xyz/light/one

I just want to compare the

"/light/one" part

5

Do you just want to know if it is in there or also where it is?

For the first, use UKHeliBob's advise.

6

I just need to know if it is there.

once it is compared and is TRUE,

it will enter a loop and other functions will be performed

7

strstr()

Worked!!!

Thank You very much people!!

8

The return value from strtstr() will give you the position of the string in the target if you need it.

9

Shantanu24:
I tried

topic.substring(14,27) == "certain string"

But it gives an error. Obviously because I am trying to SUBSTRING a *CHAR type.

Perhaps try something like

if (strstr(topic,"certain string")==topic+13) ...

The strstr function is a standard function within standard-C libraries to find a (nullterminated) string within another (nullterminated) string. This function is also available within the Arduino IDE.