[Icc-avr] Are 'local' vars in main automatuc or in bss?

[David Brown]

Hi Ton,

Although it's not actually necessary, I always use "extern" for function 
declarations in headers, for consistency with declarations for variables 
- I don't know if there is any difference between the two.

And in localfunc, you misspelled "static" :-)

mvh.,

David


Jaspers, Ton wrote:
> moduleX.h:
> 
> 	#ifndef __moduleX_h__
> 	#define __moduleX_h__		      /* avoids multiple inclusion */
> 
> 	typedef enum
> 	{
> 		HARD_TYPE,
> 		SOFT_TYPE,
> 		SEMI_SOFT_TYPE
> 	} type_t ;
> 
> 	typedef struct { type_t type, int value } global_t ; 
> 
> 	extern global_t globalvar ;		/* try to avoid these */
> 
> 	void interfacefunction(void) ;
> 
> 	#endif  /* end of #ifndef __moduleX_h__ */
> 
> moduleX.c:
> 
> 	#include "moduleX.h"
> 	#define public				/* replaced with "", for readability only */
> 
> 	static int variabvle_one ;		/* scope limited to this module */
> 	public global_t globalvar ;		/* try to avoid these */	
> 	
> 	static void localfunc ( void )
> 	{
> 	  statif first = 1 ;			/* scope limited to this function */
> 	  int count ;				/* automatic (on stack) will be destroyed after return */
> 	
> 	  if ( first )
> 	  {
> 		first = 0 ;
> 		....
> 	  }
> 	  .....
> 	}
> 
> 	public void interfacefunction(void) 
> 	{
> 	   .....	
> 	   localfunc() ;
> 	}
> 
> Hope this helps,
> Ton
> 
> 
>> -----Original Message-----
>> From: icc-avr-bounces at imagecraft.com 
>> [mailto:icc-avr-bounces at imagecraft.com] On Behalf Of Bengt Ragnemalm
>> Sent: vrijdag 26 oktober 2007 11:26
>> To: 'Discussion list for ICCAVR and ICCtiny Users. You do NOT 
>> need tosubscribeto icc-announce if you are a member of this.'
>> Subject: SV: [Icc-avr] Are 'local' vars in main automatuc or in bss?
>>
>> David, can you show us in an example how it should be done? I 
>> try to do just as you describe but I often step into problems 
>> with error like double defines and so on. 
>> I have tried using the typical #ifdef MAIN and so on but have 
>> failed making it work properly. I usually have a header file 
>> for every c file (that should be the very basics) and in that 
>> header file I put declarations on the functions. The header 
>> file is included in every other file that uses the functions. 
>> I think one reason for my problems may be that I usually in 
>> the "project.h" (there my main is) have a lot of constants 
>> and maybe some typedef that I want the other files be aware 
>> of so I include it in all other project files (not reused 
>> files like drivers). The compiler do not like that I put 
>> extern everywhere, as it is used even in my project.c. I do 
>> not want to explicity write in every global variable in the 
>> c-files (extern nn), I want to just include a .h file, I hope 
>> that is the normal procedure.
>>
>> You can expand my little example in any way you like. I tried 
>> to use self-descriptional names. There should I put the 
>> extern and there should I put the typedef customType?
>>
>> /Bengt
>>
>>
>> To be placed somewhere:
>> typedef customType...
>> #define A_VALUE 1
>>
>>
>> Project.h
>> =========
>> ??? what should be in here?
>>
>>
>> Project.c
>> =========
>> static char projectFileGlobalVar;
>> char globalVar1;
>>
>> customType globalCustomVar;
>>
>> void AFunctionInProject(void)
>> {
>> }
>>
>> void main(void)
>> {
>>   char projectFunctionLocalVar;
>>
>>   projectFunctionLocalVar = A_VALUE;
>>   projectFileGlobalVar = A_VALUE;
>>   globalVar1 = A_VALUE;
>>   globalVar2 = A_VALUE;
>>   globalCustomVar = A_VALUE;
>> }
>>
>>
>> Module.h
>> ========
>> ??? what should be in here?
>>
>>
>> Module.c
>> ========
>> static char moduleFileGlobalVar;
>> char globalVar2;
>>
>> void AFunction(void)
>> {
>>   Char moduleFunctionLocalVar;
>>
>>   moduleFunctionLocalVar = A_VALUE;
>>   moduleFileGlobalVar = A_VALUE;
>>   globalVar1 = A_VALUE;
>>   globalVar2 = A_VALUE;
>>   globalCustomVar = A_VALUE;
>> }
>>
>>
>>> -----Ursprungligt meddelande-----
>>> Från: icc-avr-bounces at imagecraft.com [mailto:icc-avr- 
>>> bounces at imagecraft.com] För David Brown
>>> Skickat: den 26 oktober 2007 10:28
>>> Till: Discussion list for ICCAVR and ICCtiny Users. You do NOT need 
>>> tosubscribe to icc-announce if you are a member of this.
>>> Ämne: Re: [Icc-avr] Are 'local' vars in main automatuc or in bss?
>>>
>>> Graham Whyte wrote:
>>>> main() is no different from any other subroutine except 
>> that it gets 
>>>> called at startup
>>>>
>>>> Variables declared outside subroutines or functions in any module 
>>>> file are Global within that module The can be referenced from 
>>>> anywhere within that module
>>> Correct up to here...
>>>
>>>> To make them Global to other modules, each other module needs to 
>>>> declare then as External
>>> That's wrong, and very misleading.
>>>
>>> Variables (and functions) get global linkage if they are defined at 
>>> file scope without "static" - C defaults to making them global and 
>>> externally accessible.  Thus two "int x;" definitions at 
>> file scope in 
>>> two modules refer to the same variable at the same address, 
>> regardless 
>>> of any "extern" declarations.
>>>
>>> The point of "extern" is to tell the compiler about a 
>> global variable 
>>> (or function) without defining it - it allows access to a global 
>>> variable, but does not turn a variable into a global one.
>>>
>>>> This is exactly the same as making a subroutine available to other
>>> modules
>>>> The declarations must of course be identical
>>>>
>>> The declaration *should* be identical - but be careful, because C 
>>> allows you to get it completely wrong and still be legal C.
>>>
>>>> You can make this very neat and tidy by putting the Globals in a 
>>>> separate module Then create the external  declarations in 
>> a separate 
>>>> header file which you can #include wherever you need You 
>> then only 
>>>> got one copy to worry about
>>> I've seen programs made like this - as Ton says, "Yuck!".
>>>
>>> If you want to write programs that are readable, understandable, 
>>> debugable and maintainable, and allow for at least some level of 
>>> re-use between programs, then you will avoid this setup 
>> like the plague.
>>> Modularisation is critical to writing software.  Break your program 
>>> into parts that fit logically together, and figure out what 
>> data and 
>>> functions (and types, macros, etc.) that module makes available to 
>>> other parts of the whole program.  This information is your 
>> module's 
>>> interface, or API, and forms its "module.h" header file.
>>>
>>> The header file "module.h" contains comments about how to use the 
>>> module, along with all type declarations, #define's, "extern"
>>> declarations of data and functions, and any #include's that 
>> are needed 
>>> to *use* the module (for example, if it contains a line "extern 
>>> uint8_t count;", then it should also contain a line "#include 
>>> <stdint.h>" or equivalent).
>>>
>>> The C file "module.c" contains the *implementation* of the 
>> module, and 
>>> has #include "module." near the beginning.  Every 
>> file-scope variable 
>>> or function is either private to the module, and defined "static", 
>>> *or* it has a corresponding "extern" declaration in 
>> "module.h".  There 
>>> should be no exceptions (except perhaps temporarily to aid 
>> debugging, 
>>> since you can see non-static items in the map file).
>>>
>>>
>>> As I said in an earlier post, I tend to rant a bit and treat my 
>>> methods as the only correct methods, but in this case there 
>> is no real doubt.
>>> If you look at any other properly structured programming language, 
>>> such as Pascal, Modula 2, or Ada, you'll see that this is 
>> exactly the 
>>> way good modular programming is always done - other 
>> languages enforce 
>>> these rules.
>>>
>>> mvh.,
>>>
>>> David
>>>
>>>
>>>> Graham
>>>>
>>>> -----Original Message-----
>>>> *From:* icc-avr-bounces at imagecraft.com 
>>>> [mailto:icc-avr-bounces at imagecraft.com]*On Behalf Of 
>>>> *bobgardner at aol.com
>>>> *Sent:* 25 October 2007 14:30
>>>> *To:* icc-avr at imagecraft.com
>>>> *Subject:* [Icc-avr] Are 'local' vars in main automatuc or in bss?
>>>>
>>>> Great summary of 'static' vars.... I remember in pascal the scope 
>>>> 'nested' and stuff 'up a level' was visible, but c doesnt allow 
>>>> nested functions I guess. Just to clarify, if I declare vars in 
>>>> main, are they local or in the bss? Is main a subroutine that is 
>>>> called with params and returns a value? Is the iccavr 
>>>> microcontroller model different from a ram based system 
>> with an os?