Pic very basic C18 question

I'm pushing along trying to learn some C using MCC18. Can someone please 
tell me what the "&" before the variable "variable" does or means in the 
code below? I'm finding it hard to find basic info like this in the 
documentation I've found.

Is it AND? AND with what?

thanks



    ee_read_byte(0x00, &cal_var); //initialise calibration variable from 
eeprom

why the "&" -----------^




unsigned char ee_read_byte(unsigned char address, unsigned char *_data){
    EEADR = address;
    EECON1bits.CFGS = 0;
    EECON1bits.EEPGD = 0;
    EECON1bits.RD = 1;
    *_data = EEDATA;
} 

Royston Vasey wrote:
> I'm pushing along trying to learn some C using MCC18. Can someone please 
> tell me what the "&" before the variable "variable" does or means in the 
> code below? I'm finding it hard to find basic info like this in the 
> documentation I've found.
> 
> Is it AND? AND with what?
> 
>     ee_read_byte(0x00, &cal_var); //initialise calibration variable from 
> eeprom
> 
> why the "&" -----------^

read as: "address of" ...

> unsigned char ee_read_byte(unsigned char address, unsigned char *_data){

... because this expects a pointer (i.e., an address) ------------^^^^

>     EEADR = address;
>     EECON1bits.CFGS = 0;
>     EECON1bits.EEPGD = 0;
>     EECON1bits.RD = 1;
>     *_data = EEDATA;
> } 
> 
> 

On 15/03/2010 05:26, Royston Vasey wrote:
> I'm pushing along trying to learn some C using MCC18. Can someone pleas=
e=20
> tell me what the "&" before the variable "variable" does or means in th=
e=20
> code below? I'm finding it hard to find basic info like this in the=20
> documentation I've found.
>=20
> Is it AND? AND with what?
>=20
> thanks

<snip>

I don't think you can learn C very efficiently by posting questions to
ask what the syntax does.  The normal and more efficient method is to
read a book.  If that is too old fashioned, then try Google:

http://home.netcom.com/~tjensen/ptr/pointers.htm

--=20

Regards,
Richard.

+ http://www.FreeRTOS.org
Designed for Microcontrollers.  More than 7000 downloads per month.

+ http://www.SafeRTOS.com
Certified by T=DCV as meeting the requirements for safety related systems=
=2E

Royston Vasey wrote:

> I'm pushing along trying to learn some C using MCC18. Can someone please 
> tell me what the "&" before the variable "variable" does or means in the 
> code below? I'm finding it hard to find basic info like this in the 
> documentation I've found.

That's because you've either been looking for the wrong kind of 
documentation, or you've tackled this whole "learning a programming 
language" task entirely the wrong way round.

What you actually need is introductory documentation of the C 
programming language, a.k.a. a C textbook.  The 2nd edition of the one 
by Kernighan & Ritchie, who invented the language, is still among the best.

And the right order of things is not to jump in and try to understand 
existing code by guessing what each letter in it means, but to actually 
_learn_ the language first, then apply that knowledge to existing code.

Royston Vasey wrote:
> I'm pushing along trying to learn some C using MCC18. Can someone please 
> tell me what the "&" before the variable "variable" does or means in the 
> code below?

This symbol means "the one with a tail should go down from the tree".

VLV

Hi Vladimir,

Vladimir Vassilevsky wrote:
> 
> Royston Vasey wrote:
>> I'm pushing along trying to learn some C using MCC18. Can someone 
>> please tell me what the "&" before the variable "variable" does or 
>> means in the code below?
> 
> This symbol means "the one with a tail should go down from the tree".

ROTFL!

On Mar 14, 10:01=A0pm, D Yuniskis <not.going.to...@seen.com> wrote:
> Royston Vasey wrote:
> > I'm pushing along trying to learn some C using MCC18. Can someone pleas=
e
> > tell me what the "&" before the variable "variable" does or means in th=
e
> > code below? I'm finding it hard to find basic info like this in the
> > documentation I've found.
>
> > Is it AND? AND with what?
>
> > =A0 =A0 ee_read_byte(0x00, &cal_var); //initialise calibration variable=
 from
> > eeprom
>
> > why the "&" -----------^
>
> read as: "address of" ...
>

I always wonder why they did not use @.  It would have been much
clearer.  After all, it was designed by a committee of two only.

"Hans-Bernhard Br&#4294967295;ker" <HBBroeker@t-online.de> wrote in message 
news:hnl8hm$i14$00$1@news.t-online.com...
> Royston Vasey wrote:
>
>> I'm pushing along trying to learn some C using MCC18. Can someone please 
>> tell me what the "&" before the variable "variable" does or means in the 
>> code below? I'm finding it hard to find basic info like this in the 
>> documentation I've found.
>
> That's because you've either been looking for the wrong kind of 
> documentation, or you've tackled this whole "learning a programming 
> language" task entirely the wrong way round.
>
> What you actually need is introductory documentation of the C programming 
> language, a.k.a. a C textbook.  The 2nd edition of the one by Kernighan & 
> Ritchie, who invented the language, is still among the best.
>
> And the right order of things is not to jump in and try to understand 
> existing code by guessing what each letter in it means, but to actually 
> _learn_ the language first, then apply that knowledge to existing code.

Thanks for the reply. I dont doubt you are correct with your comments re my 
approach!     :) 

"D Yuniskis" <not.going.to.be@seen.com> wrote in message 
news:hnkhol$rsc$1@speranza.aioe.org...
> Royston Vasey wrote:
>> I'm pushing along trying to learn some C using MCC18. Can someone please 
>> tell me what the "&" before the variable "variable" does or means in the 
>> code below? I'm finding it hard to find basic info like this in the 
>> documentation I've found.
>>
>> Is it AND? AND with what?
>>
>>     ee_read_byte(0x00, &cal_var); //initialise calibration variable from 
>> eeprom
>>
>> why the "&" -----------^
>
> read as: "address of" ...
>
>> unsigned char ee_read_byte(unsigned char address, unsigned char *_data){
>
> ... because this expects a pointer (i.e., an address) ------------^^^^
>
>>     EEADR = address;
>>     EECON1bits.CFGS = 0;
>>     EECON1bits.EEPGD = 0;
>>     EECON1bits.RD = 1;
>>     *_data = EEDATA;
>> }

thanks for that. 

>> What you actually need is introductory documentation of the C programming language, a.k.a. a C 
>> textbook.  The 2nd edition of the one by Kernighan & Ritchie, who invented the language, is still 
>> among the best.
>
> Thanks for the reply. I dont doubt you are correct with your comments re my approach!     :)


As a hardware engineer who 'did some C at university' I found 'Practical C
Programming' (O'Reilly) very good.



Nial.