Code Question and Recommendation on Good C Book

edbfmi1 · Joined: 18 Jul 2006 Posts: 103

I have a question as to what the & in the int8 declarations in the function below does.

Also I am new to C programming (not a student as someone thought) just an old analog engineer trying to keep my grey matter from hardening.

Can anyone recommend a good book on C programming as it relates to the CCS compiler and microchip? I bought the "PICmicro MCU C" by Nigel Gardner but I need something with a little more meat to it.

Thanks for everyones support.

rwyoung · Joined: 12 Nov 2003 Posts: 563 Location: Lawrence, KS USA

C language in general:

The C Programming Lanugage, 2nd Ed. by Kernighan and Ritchie.

And I'd switch your function to use

dyeatman · Joined: 06 Sep 2003 Posts: 1934 Location: Norman, OK

a quick Google gives this:

In both C and C++, the ampersand is also used at the start of a variable name to reference to the memory address of that variable in order to change the variable's value. This means they are passing the address of the variable.

GOOGLE is your friend!

K&R C is a great book that most of us have. You can get it from Amazon for almost nothing.

P.S. Sorry Rob, you just beat me to it.....

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

The method of passing the parameters with the '&' sign is named 'call by reference'. It is method for passing parameters of which you want to change and return the contents to the caller. As already indicated by the other posters it is similar to passing pointer parameters but the resulting code is easier to read because you don't have to ' dereference' the pointers.

Ttelmah · Guest

You have to be a bit careful with 'call by reference'. It is an extension to basic C, and in CCS, only implemented in a _very_ limited way. It's advantage, is that as shown, with a single function used (or with multiple functions, if these are coded as 'inline'), it will result in the subroutine directly accessing the variables 'passed', without using address calculations at all, and will result in smaller/faster code. Basically the compiler 'hard codes' the referenced address, into the subroutine. However if multiple calls to the routine are made, and these are seperate, then using the 'traditional' pointer form is safer in CCS.

Best Wishes

rwyoung · Joined: 12 Nov 2003 Posts: 563 Location: Lawrence, KS USA

RJ gave a better (and shorter) answer than I could.

I have had much less trouble with "odd" code when using int *num_monkeys than int &num_monkeys with the CCS compiler(s).

This does bring up two good points for beginners (all of us for that matter), and they are:

Always look at your LST file to see how the compiler did something.

And, be able to at least READ the assembly listings. Better if you can write in assembly too but at least be able to read a section of code and understand what is happening.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month!

newguy · Joined: 24 Jun 2004 Posts: 1909

"Embedded C Programming and the Microchip PIC" by Barnett, Cox and O'Cull. Pretty good book, and it does deal with the CCS compiler. Even comes with a demo version of the compiler on CD.

arnfielb · Guest

Good book is "The Indispensible Guide to 'C'" - written for students and contains many real world embedded C examples and including practical examples of interfacing to hardware. This book is not PIC specific.
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