Strcmp not working with multiple conditions combined with logical OR statement ( || )

Projects Programming
1

Hello. I would like some guidance regarding multiple strcmp statements. I have found a simmilar post but the issue not been solved:

I have a variable item_inside.state. I want to compare whether it is set to "PILDYMAS" or "DISABLED" and if it is not either 2 of those, I want to read the sensor, else dont read the sensor.

I can easily do this with the following code;

 if( strncmp(item_inside.state, "DISABLED", 8)  !=0 ) 
  {
    Read_sensor_no_delay(tft_object);
  }

 if( strncmp(item_inside.state, "PILDYMAS", 8)  !=0 ) 
  {
    Read_sensor_no_delay(tft_object);
  }

However, it would be much more clean if I could do :

  if( (strncmp(item_inside.state, "PILDYMAS", 8)  !=0)  ||  (strncmp(item_inside.state, "DISABLED", 8)  !=0) )  
  {
    Read_sensor_no_delay(tft_object);
  }

Unfortunately, the above code just does not work. Even though I have set my state to "PILDYMAS" or '"DISABLED" it still performs read_sensor_no_delay function.

Has anyone else faced this issue? Can this be fixed?

2

The logical expression state ≠ "A" or state ≠ "B" can never evaluate to false, because state cannot be equal to "A" and "B" simultaneously.

(By the way, if this is some kind of state machine, use an enum, not C-strings.)

3

Hey. Thanks for the response. I cannot fully get my head around on what you said. Now I do not know anymore whether I understand IF statement correctly. For example if my state is "IDLE" and I compare it with both "PILDYMAS" and "DISABLED", then the comparison !=0 will be TRUE because "IDLE" is not equal to "PILDYMAS" or "DISABLED". However, if I set my state to "DISABLED" and then do comparison, since one of the condition in if statement is met , it should return false. The same with the following:

The following will return true because one of the contition is met

x = 5
if (x==5) || or (x==6)

The following will return false

x=4
if (x==5) || or (x==6)

Why is this not the same in my case?

4

if fruit is not pear or fruit is not banana then eat fruit.

Try the above sentence with "apple" and "pear" for the fruit.
It is the combination of != with ||

The strncmp() returns zero when they are equal: https://www.cplusplus.com/reference/cstring/strncmp/

5

Ahhh now it totally makes sense... Thank you very much!