How to clear static IP configuration and start DHCP

Question

I'm using a sketch like this:

WiFi.config(IP, Gate, Subnet);
WiFi.begin (ssid, pass);

//-- somewhere below I want to drop the static IP configuration and obtain IP with DHCP.

WiFi.disconnect ();
WiFi.begin (ssid, pass). //ssid and pass are the same as above.

But IP is not changing. It seems that WiFi hasn't been reconnected. How to drop static IP configuration without restart? I'm using nodemcu v3 with esp8266 -12e.

Answer 1

You are right. There is a DHCP issue at Arduino firmware. When I did checked from the WiFiSTA firmware implementation, I saw that staticIP flag get set once when you call config() function and never get cleared. This flag guards the DHCP start/stop operations. So, here is a solution for you. Just add the ESP SDK header to your code like:

extern "C" {
  #include "user_interface.h"
}

Now you are able to call dhcp start function from firmware which was previously blocking by the flag. But, notice that you have to call it after WiFi.begin() with some delay. Use the code block below:

WiFi.disconnect(true);
delay(1000);
WiFi.begin(ssid, pass);
(void)wifi_station_dhcpc_start();

Answer 2

This should really be a comment to the accepted answer but my reputation is not high enough... Anyways, as noted in that answer there is a built in option for resetting the staticIP flag, but the trick to making it work is that the arguments need to be unsigned. I.e. WiFi.config(0u, 0u, 0u);. Should the unsigned part be omitted, you get the "conversion from 'int' to 'IPAddress' is ambiguous" error mentioned in the accepted answer's comments.

Looking at the source for the Arduino firmware's station class one can see that WiFi.config(0u, 0u, 0u); actually changes a protected flag in addition to executing wifi_station_dhcpc_start(), so I would say that using WiFi.config(0u, 0u, 0u); is the way to go.