Lpc2000

Hello,

why you do you declare a string in that way?

	char * f = "Hello";

'char* f' declares only a pointer to something. In this declaration
"Hello" should be treated as constant char array by the compiler. Does
the compiler complains about assigning const to non-const if you turn on
-Wall???
Correct way to declare a pre-defined char array containing "Hello" would be:

	char f[] = "Hello";

That's a different! May the first line result in some confusions in the
compiler?!?

  Sten


Robert Adsett wrote:
> At 01:51 AM 10/18/05 +0000, embeddedjanitor wrote:
> 
>>--- In lpc2000@yahoogroups.com, "Guillermo Prandi" <yahoo.messenger@m
>>...> wrote:
>>
>>>I too gave a suspicious look at the startup code. But the thing is,
>>>in order to copy the modifiable data to RAM it must be in the ROM in
>>>the first place! It doesn't show in the lst file, whilst puts()
>>>parameters do.
>>
>>They will be in a different area.
> 
> 
> Good point.
> 
> 
> 
>>A constant string will be on the rommable constants area (.rodata in
>>GNU talk).
>>
>>A modifiable string will be in the data initialisation section (.data
>>in GNU talk). This is rommed, but is copied into RAM for the
>>execution.
>>
>>
>>>I tried giving a const to the function's declaration, with no luck.
>>
>>No luck expected :-). consting a function just says that the function
>>will not try to modify the string that it is passed. It does not
>>modify the placement of the string.
> 
> 
> But it will make a difference in this case.
> 
> Case 1:
> void myfun( char *);
> 
> myfun("test");
> 
> In this case we have a pointer to a modifiable string and therefore in ram.
> 
> Case 2:
> 
> void myfun( const char *)
> 
> myfun("test");
> 
> In this case we have a pointer to a non modifiable string and which can be 
> in flash.  If this isn't true then printf wouldn't work given your above 
> and the OP has already stated that
> 
> printf("test");
> 
> works.
> 
> In the third case
> 
> void myfun( const char *);
> void myfun2( char *);
> char * f = "test";
> 
> myfun(f);
> myfun2(f);
> 
> The source is the same and whether the argument is const makes no difference.
> 
> I think your diagnosis is likely right unless Case 2 above behaves 
> differently then printf.  If it does something else is going on.
> 
> 
>>>However, I narrowed down the problem to auto-inlining: if I move the
>>>do_something() function to another source (I was testing with an
>>>empty body on the function!), the strings do show in the .data. This
>>>kinda makes sense, since the compiler realized that there was no
>>>point for that constant to be in the code in the first place. What
> 
> 
> Um, well yeah, with
> 
> static void myfunc( const char *)
> {
> }
> 
> func()
> {
> myfunc("test");
> }
> 
> the compiler could quite legitimately optimize myfunc out of 
> existence.  Even if it wasn't declared as a static function the compiler 
> could optimize the call away and leave the hook for any external callers. I 
> was sort of assuming you actually did something with the string, otherwise 
> how would you notice?  Checking for a Copyright in the image maybe?
> 
> Robert
> 
> 
> " 'Freedom' has no meaning of itself.  There are always restrictions,   be 
> they legal, genetic, or physical.  If you don't believe me, try to chew a 
> radio signal. "  -- Kelvin Throop, III
> http://www.aeolusdevelopment.com/
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
> 


-- 
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