How to know the frequency of AP mode

[Grégoire Gentil]

My question is summarized here:

https://stackoverflow.com/questions/47398018/hostapd-how-to-know-the-frequency-of-ap-mode


"On Linux, I'm using hostapd in AP mode. In other words, the system is 
the hotspot.

I would like to know what is the frequency of the Wi-Fi via c code (or a 
bash script that I could translate to c code).

The following code which queries the kernel, only works in normal mode. 
It fails in AP mode.

ioctl(net_sock, SIOCGIWFREQ, &wrq);

In bash, I have tried:

iwconfig
iw dev

but it doesn't report the frequency of the Wi-Fi. Same problem: it only 
reports in normal mode when the system associates to a router but 
nothing in AP mode.

How can I query hostapd to know the frequency hostapd is using or is 
configured to use?"


Grégoire