Basically, you have a concatenation of 3 sets of libraries, builtin (constant), hardware that changes with the board selected (as well as examples) and the Custom Libraries you have installed through either Tools/Manage Libraries or Sketch/Include Library/Add .ZIP Library... which are mostly github zip files downloaded to your PC.

It's all documented in the Arduino.cc site under Libraries.

I'm afraid Python has taken over for me for GUIs because it will run on so many platforms.

I have yet to look at Python.   For a while things got crazy with all the languages.  Shell, C, C++, Java, Pearl, PHP, SQL now Python.   I just decided to stick with C.   The software business has a way of taking over a persons life.    The idea of a small controller board with basically only my code is very appealing.   At some point I may have to dig into Python since it seems to have a solid foot hold.

Big smile time ! A long time ago I wrote a package for a big machine tool in Turbo Pascal. Basically a big database to create machining lists for timber components. As part of the contract the company got the source code. The company had an ex-lecturer as head of IT and he had a real go at me, "that is terrible code, there are not enough comments". I replied "Pascal is self documenting". "Rubbish" he said. I later realised he was right. As a young man I could almost type out all the code from memory but I learned that that memory does not last. He was right.

What an incredible product Turbo Pascal was. Until then all I had was BASIC. So this would have been 1983(ish).

Then came Delphi which was deep joy to write Windows programs in.

I even have a load of Lazarus on this PC, for old time's sake, but I've not used it in anger. I'm afraid Python has taken over for me for GUIs because it will run on so many platforms.

Having no background with these micro controllers,  I was wondering if they had a flat address space and I might be able to load any address in that space into a pointer.   No matter, you answered the question in that  malloc is the way to do it.  I'm sure I have many misconceptions which I will work through. Thanks. 

Please don't feel that you have to stop asking questions here.

If you run into anything that you can't find or answer from The Arduino site's documentation or a Google search, then by all means post your question. We are here to help you.

Just google what you are interested in, trying several searches with different words. You will recognize when you have found the docs, for Espressif they have that in the URL, and similarly for Arduino.

Yes, you have 2K for variables and 16K or more for programming (depending on Arduino model). I'm sure you can use malloc, although I've never had to on an Arduino. Remember, it's a 'toy' compared to a bare bones laptop. You may find it a challenge to keep your design within the constraints.

Again, you're dealing with a single core (and slow by today's standards) processor. Multi-threading is contra-indicated :) You can, however use timer and pin-based interrupt routines.

You're in for a shock moving from "big multitasking virtual memory based operating systems" down to an Arduino but it's not like you're co-ordinating a warp engine.

What kind of projects are you envisioning (in the long run when you're up to speed). It's possible that you may need to consider using an SBC (single board computer) such as a Raspberry Pi instead of an Arduino.

in a simple sketch (why a program in now called a sketch seems odd)

So, really, you're just adding some code to an existing code set - it's not really a 'program' since it's controlled via a means that you never see nor have control over.  

Okay, I think I can see what you mean and I guess is doesn't really matter what executable code is called.

Another item I forgot to ask.   Am I correct in assuming this in a flat memory fixed address space system, static ram and flash.  No virtual memory or address space.   I don't need a malloc function, I can just create a pointer, load an address and fill a structure using that pointer? 

Are there execution threads available?   Like loop on a connection_request, start a process for that event then continue listening for the next event. 

I have never worked on anything but big multitasking virtual memory based operating systems.  

I promise I will stop with the questions, for now anyway until I dig in to stuff for a while.  I'll pickup a board and give it a shot.

Thank you all or your input.