Not Keil specific; one for the 'C' experts:
Why would one put 'static' variables definitions in a header?
eg, in a header file:
/* * TCO count to temperature conversion table. */ static erTcoTableStruct tcoTableOPUS1[] = { /*{TCO,Temp,} */ {1,-99}, {4,-45}, {5,-40}, {8,-35}, {11,-30}, {16,-25}, {22,-20}, {29,-15}, {37,-10}, {48,-5}, {61,0}, {78,5}, {99,10}, {124,15}, {153,20}, {188,25}, {227,30}, {270,35}, {315,40}, {365,45}, {420,50}, {481,55}, {549,60}, {625,65}, {710,70}, {805,75}, {910,80}, {1010,85}, {1060,88} };
AIUI, the whole point of so-called "header" files in 'C' is to share stuff between source files;
But the whole point of the 'static' keyword (at file scope) in 'C' is to make stuff private so that it is not visible to other modules - ie, not shared.
So I can't see why one would want to have 'static' definitions in a header?!
It is also potentially a waste of memory - every inclusion of the header file will instantiate a copy of the static variable in it.
I don't think that's just "potentially" - it's for certain!
Especially in cases like the example I showed - which is quite a large table!!
Thanks!
"The only halfway sensible reason I can come up with (which I think someone else already suggested) is to allow the instance of the struct local to each source file to modify its local instance at runtime."
Yes - Mike Kleshov suggested it.
Anyone (else) got any other ideas?
The questions was why anyone would want to do it?
Far more likely than not because they have no idea what they're doing.
Just because there are people doing something doesn't mean that valid reasons exist for doing it.
Yes, that is very much the impression I get from the code in question!
:-(
"Just because there are people doing something doesn't mean that valid reasons exist for doing it."
Indeed! But I wanted a "second opinion" - in case there was a valid reason that I just hadn't thought of!
Static has three distinct uses in C:
Not really. It has two distinct uses: it changes linkage from external to internal, or duration from automatic to static.
(2) A variable declared static within a module, (but outside the body of a function) is accessible by all functions within that module. It is not accessible by functions within any other module. That is, it is a localized global.
(3) Functions declared static within a module may only be called by other functions within that module. That is, the scope of the function is localized to the module within which it is declared.
These two are the same thing, really. Distinguishing between functions and variables serves no purpose in this case. 'static' limits the visibility of external definitions to the containing translation unit, regardless if those definitions are of variables or functions.
Interestingly, the header mentioned in my original post does also contain static function declarations!
AFAIKS, this really makes no sense at all, since it forces every file which includes the header to provided a definition of the function - otherwise you get a "function declared static but not defined" warning!
Again, this suggests to me that the only reason for all this is, in fact, that the author(s) had no idea what he/she/they were doing!
See reference above:
* Incompetence * Sloth * A bad character * Job security * Arrogance
I did a search of my active projects for the word "static" and looked for 'extern' in front of it.
I found eight out of 712 'statics'. [oops] http://i.imgur.com/CVowH.jpg
A note here: TheBCS project isn't finished and is currently on the back-burner (still on the stove though), so I *might* have debugged those out.
--Cpt. Vince Foster 2nd Cannon Place Fort Marcy Park, VA
P.S. Happy Easter!! (The celebration of the resurrection of Jesus Christ)
this is actually a different question.
There are no externs in my question; just statics in a header file.
PS. Yes, Happry Easter!
"He is risen indeed!"
Andy,
With all due respect, and after much ado, I shall answer that question of "why put 'static' in a header file?"
Simple. ALL data-allocation on a module-wide basis should be declared/allocated within its associated header file. ALL external data-references should also be in it's [external] associated .C file's header.
ONLY routine/function specific data-store should be allocated within the actual .C file.
That's my philosophy, and I'm sticking to it.
A #define MAX_SIZE would also be in that header file, so your 'static UART_Buffer[ MAX_SIZE ]; is clearly identified within that .H file.
OK - if that is your philosophy, that's fair enough.
But, presumably, this requires a mechanism to ensure that "file-local" (ie, "internal linkage") variables are not repeated in other files?
Thanks for the 'fair enough' comment.
And yes, the "required" mechanism is my
#ifdef UART_Module // Data Allocation #else // Data reference #endif
construct.
(Not to mention my "uber" #include "Headers.H" file total control freak method of inclusion).
But that's where it gets a bit confusing!
The whole point of making something static is so that it can not be externally referenced!
So, in this case, would you have, say:
#ifdef UART_Module static char private_uart_char; #else // No reference for private_uart_char #endif
yes?
Perhaps you could clarify what you mean by "module" here?
Is it a single compilation unit, or the collection of files which, together, form a "module"?
eg, if your UART "driver" consists of, say, a uart_input.c, a uart_output.c and a uart_isr.c - do you consider that to be three "modules", or one?
Yes, you are correct. There would be no extern static UART_Buffer[ MAX_SIZE ];
Even though I am unsure as to the invalidity of doing so, generally I wouldn't do it. My prior post (with he link to the picture) showed that I did make 'extern static' data references. I don't remember why I was doing so. But out of 700+ only eight were of that type in an unproven code-monkey fragment.
--Cpt. Vince Foster 2nd Cannon Place Fort Marcy Park, VA P.S. I've really got to move my house now... later for a while.
Here's what VC thinks of that:
error C2159: more than one storage class specified
Did you compile that code at all?
If I've managed to unpick your explanation of your header file usage you seem to define all file scope variables in a header file and all function scope variables in the function. That doesn't make a lot of sense - why hide file scope declarations in a separate file, particularly if they are not referenced outwith that file?
More than anything else, though, there's no point in ignoring convention unless you have a compelling reason to do so, and the reasons you have given so far are not compelling. They add up to little more than 'I do it my way because it's my way'.
View all questions in Keil forum