WiFi.scan, scan

Returns information about access points within range of the device.

The first form is the simplest, but also least flexible. You provide a array of WiFiAccessPoint instances, and the call to WiFi.scan() fills out the array. If there are more APs detected than will fit in the array, they are dropped. Returns the number of access points written to the array.

// EXAMPLE - retrieve up to 20 Wi-Fi APs
SerialLogHandler logHandler;

WiFiAccessPoint aps[20];
int found = WiFi.scan(aps, 20);
for (int i=0; i<found; i++) {
    WiFiAccessPoint& ap = aps[i];
    Log.info("ssid=%s security=%d channel=%d rssi=%d", ap.ssid, (int)ap.security, (int)ap.channel, ap.rssi);

The more advanced call to WiFi.scan() uses a callback function that receives each scanned access point.

// EXAMPLE using a callback
void wifi_scan_callback(WiFiAccessPoint* wap, void* data)
    WiFiAccessPoint& ap = *wap;
    Log.info("ssid=%s security=%d channel=%d rssi=%d", ap.ssid, (int)ap.security, (int)ap.channel, ap.rssi);

void loop()
    int result_count = WiFi.scan(wifi_scan_callback);
    Log.info("result_count=%d", result_count);

The main reason for doing this is that you gain access to all access points available without having to know in advance how many there might be.

You can also pass a 2nd parameter to WiFi.scan() after the callback, which allows object-oriented code to be used.

// EXAMPLE - class to find the strongest AP

class FindStrongestSSID
    char strongest_ssid[33];
    int strongest_rssi;

    // This is the callback passed to WiFi.scan()
    // It makes the call on the `self` instance - to go from a static
    // member function to an instance member function.
    static void handle_ap(WiFiAccessPoint* wap, FindStrongestSSID* self)

    // determine if this AP is stronger than the strongest seen so far
    void next(WiFiAccessPoint& ap)
        if ((ap.rssi < 0) && (ap.rssi > strongest_rssi)) {
            strongest_rssi = ap.rssi;
            strcpy(strongest_ssid, ap.ssid);


     * Scan Wi-Fi Access Points and retrieve the strongest one.
    const char* scan()
        // initialize data
        strongest_rssi = -128;
        strongest_ssid[0] = 0;
        // perform the scan
        WiFi.scan(handle_ap, this);
        return strongest_ssid;

// Now use the class
FindStrongestSSID strongestFinder;
const char* ssid = strongestFinder.scan();