BLE getValue()

// Define digital output UUID
#define OUTPUT_UUID    0x2A57

/** Characteristic for digital output */
BLECharacteristic *pCharacteristicOutput;

/**
 * MyServerCallbacks
 * Callbacks for client write requests
 */
class MyCallbackHandler: public BLECharacteristicCallbacks {
  void onWrite(BLECharacteristic *pCharacteristic) {
    std::string value = pCharacteristic->getValue();
    int len = value.length();

    if (value.length() > 0) {
      Serial.println("*********");
      Serial.print("New value: ");
      for (int i = 0; i < value.length(); i++) {
        Serial.print(String(value[i]));
      }
      Serial.println();
      Serial.println("*********");
    }
  }
};

/**
 * initBLEserver
 * Setup BLE server
 * Setup callbacks for server and pCharacteristicStatus
 * Start advertising the BLE service
 */
void initBLEserver() {
// skipped code to initialize the BLE server
	// Create BLE Characteristic for Digital output
	pCharacteristicOutput = pService->createCharacteristic(
		BLEUUID((uint16_t)OUTPUT_UUID),
		BLECharacteristic::PROPERTY_WRITE
	);
	pCharacteristicOutput->setCallbacks(new MyCallbackHandler());
// skipped code to start advertisment
}