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!!
So you can further argue your point of view??
I think this question has been answered. The developer explained the reasons for why it was used, which is more than you can usually expect from a code snippet.
It was also estabished that this is not the most efficent way to code. But, the developer seems to be in high regard within this community and I personally have no issue with the way he wants to code something. If it is a preference, and it does not violate the responsibilities entrusted to an engineer regarding safety and reliability then it is allowed.
Would I use this approach? I believe that question has also been answered.
There is no absolutely correct way to code to solve a problem. There are only more efficient and effective ways to do it. If the coding solution is accomplished within established guidelines and is well documented so be it. The fix would be easy enough: static --> const
Finally, if it is expected that someone else will post the why to this question, knowing full well the bias of this thread regarding why you should not use this approach, given a choice, do you really expect someone to do this? Only if they like to argue a point.
As far as I'm concerned, this was nothing more than an academic exersize.
Cheers.
Are you referring to Cpt Vince?
He was not the developer of the code that I cited in my original post!
I think you've got sidetracked onto a discussion of the way he manages his header files. That wasn't my original question!
My question was, what could be the point in having static definitions in a header file (irrespective of how you manage your header files); in other words, what could be the point in having multiple identically-named and identically-typed but distinct objects in the files of a project?
"As far as I'm concerned, this was nothing more than an academic exersize."
Well, I've got code like that, and I can't see any good reason for it - so I was wondering if anyone could suggest one.
Unfortunately, the discussion got sidetracked into different ways of managing headers - which wasn't the point.
I congratulate you for your persistence!
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. I'm sure someone, somewhere will have managed to find a reason to do this.
Regarding some of the other stuff in this thread:
For the confused: From the compiler's perspective include files don't exist, so special handling is not an option.
For the deluded: The convention in 'C' programming is that header files do not include any code that allocates storage. Everyone goes through the "oh but I've got this great way of using header files that's much better/safer/controlled than the usual way" during their learning curve. Fortunately most of them eventually realise that the conventional approach is the best one.
When you join a company or a project you adopt the existing conventions, even though those almost certainly aren't the best. Why would you join a community of (presumably) hundreds of thousands of 'C' programmers than decide not to follow convention?
I look forward to the responses...
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?
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