API change in the ESP32 Arduino libraries, see:

rdridder · rdridder · commit dc007d428d5b · 2024-10-12T17:16:09.000+02:00
espressif/arduino-esp32#8724 https://github.com/espressif/arduino-esp32/blob/master/libraries/BLE/src/BLECharacteristic.h std::string is now changed to String.
diff --git a/module/midi/BLE-MIDI/hardware/BLEMIDI_ESP32.h b/module/midi/BLE-MIDI/hardware/BLEMIDI_ESP32.h
@@ -113,7 +113,7 @@ class MyCharacteristicCallbacks : public BLECharacteristicCallbacks
 
     void onWrite(BLECharacteristic *characteristic)
     {
-        std::string rxValue = characteristic->getValue();
+        String rxValue = characteristic->getValue();
         if (rxValue.length() > 0)
         {
             _bluetoothEsp32->receive((uint8_t *)(rxValue.c_str()), rxValue.length());
diff --git a/module/midi/BLE-MIDI/hardware/BLEMIDI_ESP32_NimBLE.h b/module/midi/BLE-MIDI/hardware/BLEMIDI_ESP32_NimBLE.h
@@ -106,7 +106,7 @@ class MyCharacteristicCallbacks : public BLECharacteristicCallbacks
 
     void onWrite(BLECharacteristic *characteristic)
     {
-        std::string rxValue = characteristic->getValue();
+        String rxValue = characteristic->getValue();
         if (rxValue.length() > 0)
         {
             _bluetoothEsp32->receive((uint8_t *)(rxValue.c_str()), rxValue.length());

Original file line number	Diff line number	Diff line change
`@@ -113,7 +113,7 @@ class MyCharacteristicCallbacks : public BLECharacteristicCallbacks`
`113`	`113`
`114`	`114`	`void onWrite(BLECharacteristic *characteristic)`
`115`	`115`	`{`
`116`		`- std::string rxValue = characteristic->getValue();`
	`116`	`+ String rxValue = characteristic->getValue();`
`117`	`117`	`if (rxValue.length() > 0)`
`118`	`118`	`{`
`119`	`119`	`_bluetoothEsp32->receive((uint8_t *)(rxValue.c_str()), rxValue.length());`
Original file line number	Diff line number	Diff line change
`@@ -106,7 +106,7 @@ class MyCharacteristicCallbacks : public BLECharacteristicCallbacks`
`106`	`106`
`107`	`107`	`void onWrite(BLECharacteristic *characteristic)`
`108`	`108`	`{`
`109`		`- std::string rxValue = characteristic->getValue();`
	`109`	`+ String rxValue = characteristic->getValue();`
`110`	`110`	`if (rxValue.length() > 0)`
`111`	`111`	`{`
`112`	`112`	`_bluetoothEsp32->receive((uint8_t *)(rxValue.c_str()), rxValue.length());`