user62375: I am working from the example sketch in that installed with the ESP32 Dev Module into the Arduino IDE.  It includes <WiFi.h> and "time.h".  I have a number of questions about how to use the clock that is set up with configTime using NTP. I am trying to find the documentation, but I'm having difficulty identifying exactly who is providing me the "time.h" header file, and of course, there are a lot of different time.h header files out there so googling is difficult.
Where can I find the documentation for this particular header?

Example questions:

Can the time be set manually without a WiFi connection?
Can the timezone be changed without connecting to NTP again?
Can I get the time as a Unix Time Stamp?  (Yes)
Can I arrange for a function callback at a certain time? (I'm aware I can use the timer library for this but I'm hoping for something like a callback at 4:20p every Saturday)


user4143: time.h is provided by the compiler (more specifically the C library in use in the compiler).
I believe the xtensa-esp32 compiler uses newlib as the C library. If that is the case, the documentation is here: https://sourceware.org/newlib/libc.html#Timefns

62375: <p>I am working from the example sketch in that <a href="https://randomnerdtutorials.com/installing-the-esp32-board-in-arduino-ide-windows-instructions/" rel="nofollow noreferrer">installed</a> with the ESP32 Dev Module into the Arduino IDE.  It includes <code>&lt;WiFi.h&gt;</code> and <code>"time.h"</code>.  I have a number of questions about how to use the clock that is set up with <code>configTime</code> using NTP. I am trying to find the documentation, but I'm having difficulty identifying exactly who is providing me the <code>"time.h"</code> header file, and of course, there are a lot of different <code>time.h</code> header files out there so googling is difficult.</p>

<p>Where can I find the documentation for this particular header?</p>

<hr>

<p>Example questions:</p>

<ul>
<li>Can the time be set manually without a WiFi connection?</li>
<li>Can the timezone be changed without connecting to NTP again?</li>
<li>Can I get the time as a Unix Time Stamp?  (<a href="https://arduino.stackexchange.com/questions/71453/esp32-seconds-from-epoch">Yes</a>)</li>
<li>Can I arrange for a function callback at a certain time? (I'm aware I can use the timer library for this but I'm hoping for something like a callback at 4:20p every Saturday)</li>
</ul>
 4143: <p><code>time.h</code> is provided by the compiler (more specifically the C library in use in the compiler).</p>

<p>I believe the xtensa-esp32 compiler uses <em>newlib</em> as the C library. If that is the case, the documentation is here: <a href="https://sourceware.org/newlib/libc.html#Timefns" rel="nofollow noreferrer">https://sourceware.org/newlib/libc.html#Timefns</a></p>
