Comparing strings from AdafruitIO_Data object

Question

I can't seem to compare what I believe are strings.

My function looks like the following:

void handleMessage(AdafruitIO_Data *data) {
  Serial.printf("\nreceived <- %s", data->value());
  if (data->value() == "OPEN") {
    Serial.printf("\nIt worked!");
  }
}

When printed, data->value() prints what I expect it to, but when I compare it like this data->value() == "OPEN" it doesn't work. What is the right way to do this, and why isn't the above working?

I have attempted to use strcmp() as suggested by How do I properly compare strings?

void handleMessage(AdafruitIO_Data *data) {
  Serial.printf("\nreceived <- %s", data->value());
  if (strcmp(data->value() == "OPEN")) {
    Serial.printf("\nIt worked!");
  }
}

However I get:

FileName:48: error: cannot convert 'bool' to 'const char*' for argument '1' to 'int strcmp(const char*, const char*)'

It isn't a boolean when it is printed. From my example it prints: received <- OPEN

Answer 1

When printed, data->value() prints what I expect it to, but when I compare it like this data->value() == "OPEN" it doesn't work. What is the right way to do this, and why isn't the above working?

strcmp takes two arguments both are char * (pointer to a char), you are supplying it with a boolean expression that boils down to a bool

Reference for strcmp can be found here

Assuming that AdafruitIO_Data is as defined here and that you've included string.h

void handleMessage(AdafruitIO_Data *data) {
  Serial.printf("\nreceived <- %s", data->value());
  if (!strcmp(data->value(), "OPEN")) {
    Serial.printf("\nIt worked!");
  }
}