Request explaination

[Ilzam]

Hi,

Could you explain function or meaning of below coding.

// If we are connected to a peer BLE Server, update the characteristic each time we are reached
// with the current time since boot.
if (connected) {
if (onoff) {
Serial.println("Notifications turned on");
pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902))->writeValue((uint8_t*)notificationOn, 2, true);
}
else {
Serial.println("Notifications turned off");
pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902))->writeValue((uint8_t*)notificationOff, 2, true);
}

onoff = onoff ? 0 : 1;

}
`

[frownbreaker]

The question mark in the code is known as the ternary operator in C. Ternary is an adjective meaning three parts. Its a mathematical term (computer science is a branch of mathematics). It is available in many languages: https://en.wikipedia.org/wiki/%3F:

Also in the code sample you posted "onoff = onoff ? 0 : 1;" there is an = (assignment operator) rather than an == (comparison operator)

Before explaining the code you asked about you should first understand the ternary operator:

This is the typical textbook example..

//Looking at the maximum example

int findMaximum(int a, int b){
    //if a > b, it returns a, if not it returns b
    return (a > b) ? a : b;
} 

Ok so now we know what the ternary operator ? is used for we need to disambiguate == from =. In C to compare something you use "==" and to set something to a value you use "="

One last point - For the avoidance of doubt: In C true is represented by any numeric value not equal to 0 and false is represented by 0.

Ok, now that's covered! We can answer your question! The code you asked about onoff = onoff ? 0 : 1; means "if the value of onoff is true set the value of onoff to 0 otherwise set the value of onoff to 1"

Reading the code initially one might think the value of onoff is never changed from its initial value bool onoff = false;, but on inspection, the assignment is done using the ternary operator. I think many folk might have missed this subtle difference. Excellent question :) Hope this helps?

The code you provided did not have the assignment but I assumed you got the code from here nkolban/esp32-snippets#269

[1043717432]

How do you request that you compile it?
I have an error using Arduino1.85

In file included from C:\Users\eric8\Documents\Arduino\BLE_Proximity_Sensor\BLE_Proximity_Sensor.ino:23:0:

D:\homeassistant\arduino-1.8.5\arduino-1.8.5\portable\sketchbook\libraries\ESP32_BLE_Arduino-7951347ed68313d75c367e1f2cce763cb56d1eb2\src/BLEDevice.h:10:23: fatal error: sdkconfig.h: No such file or directory

  #include "sdkconfig.h"

                        ^

Compilation terminated.

Exit status 1