AW: Re: [Icc-avr] Bootloader problem PROBLEM FOUND

[David Brown]

Daub, Stephan wrote:
> Hi all,
> 
>> You must do this explicitly in your >code.
> ...But is this good programming style anyway (in all programming
> languages), isn't it ?
> 
> Best, stephan
> 

It is always important to initialise your local variables before using 
them - using a variable before it has a value assigned is not a matter 
of style, but a matter of correct code.  However, there is no need to 
explicitly initialise a variable if it is latter set before using it:

void foo(void) {
	int i = 0;		// unnecessary explicit initialisation

	for (i = 0; i < 10; i++) ...
}

For non-static local variables, there is no difference between giving a 
value when the variable is declared, and a simple assignment.  It is 
therefore often convenient to assign the initial value just before the 
variable is first used, rather than where it is declared - this may also 
lead to better code generation (on C99 compilers, you may want to leave 
the declaration until later as well, but that's a matter of style).

It is also unnecessary to explicitly initialise file-scope data that 
should start at 0 - this is done automatically, and explicit 
initialisation is a waste of space.  There are exceptions - if you have 
an enumerated type, or a variable normally used with a set of #define'd 
constants, you should probably explicitly initialise it with the 
enumeration value even if that is represented by 0.

mvh.,

David



> -----Original Message----- From: icc-avr-bounces at imagecraft.com
> <icc-avr-bounces at imagecraft.com> To: Johan Wallström <johan at edab.nu>;
> Discussion list for ICCAVR and ICCtiny Users. You do NOT need
> tosubscribe to icc-announce if you are a member of this.
> <icc-avr at imagecraft.com> Sent: Mon Nov 05 12:17:34 2007 Subject: Re:
> [Icc-avr] Bootloader problem  PROBLEM FOUND
> 
> And the global/static variables only gets initialized ONCE (at
> program start-up). No variables are initialized automagically upon
> function entry (except the argument(s) of course). You must do this
> explicitly in your code.
> 
> Regards Johan Bodin
> 
> ----
> 
> Johan Wallström wrote:
>>> If I don't initialize the TimeOut = 0; the code didn't work
>>> (that's in bootloader application)
>>> 
>>> Sylvain
>> Yeah, (uninitialized) global and static data get's initialized to
>> zero by the compiler, while (uninitialized) local data does not -
>> they get whatever value happens to be there.
>> 
>> regards Johan Wallström Elektronik Design AB +4660169550
>>