Please tell me how to use it using bluetooth_send function.

[odenwar]

I made a serial bluetooth function but I want to use it in a form like printf.

void bluetooth_send(const char *message , ... ){

  uint16_t tx_len = strlen(message);
  ble_nus_data_send(&m_nus, (uint8_t *)message, &tx_len, m_conn_handle);
  
  uint8_t crlf[2] = {10, 13};
  tx_len = 2;
  ble_nus_data_send(&m_nus, (uint8_t *)crlf, &tx_len, m_conn_handle);
  
}

 Please tell me how to use it using bluetooth_send function.

bluetooth_send("gyroscope X : %d", gyroscope_X_L); 

[awneil]

The simplest way is going to be to first prepare your string using sprintf(), and then pass that string to bluetooth_send(); eg,

char buffer[80]; // A suitably sized buffer in which to prepare you string

// Prepare the string
sprintf( buffer, "gyroscope X : %d", gyroscope_X_L );

// Send the string over BLE
bluetooth_send( buffer ) ; 

[odenwar]

Is it difficult to transfer to one function?

[awneil]

Depends on your definition of "difficult" !

Are you familiar with writing variadic functions in C ?

eg, see: https://en.cppreference.com/w/c/variadic