Here comes a very special wish - please do not call me crazy:
Working with many C modules, I prefer to define protected/"dangerous" variables static to one module. Quite often I would like to have a variable global only in a restricted number of modules - typically only in one module and then further the the communication modules (e. g. "comm1.c", "comm2.c").
To achieve this, it would be terrifically nice, if I could create the following code with a special pragma modifier (I made the examples with two modules "comm1.c" and "comm2.c", to keep the examples more general - but in fact I would be perfectly happy, if this would work with restriction to one further module "comm.c"):
#pragma RestrictedGlobal "comm1.c" #pragma RestrictedGlobal "comm2.c" int iRestricted;
(alternatively also like this (but then it would not work in other C compilers):
#pragma allowAccess "comm1.c" #pragma allowAccess "comm2.c" static int iRestricted;
)
In "comm1.c", "comm2.c" then the extern command
extern int iRestricted;
should be allowed - but it any other module it should fail (best would be, if the command itself would be allowed, but if the access to iRestricted would fail in any other module - then it is possible to include the extern declaration in some header file without the danger of failure)
I know that this is not possible in any other C compiler, but I think pragma is not standardized, so C compiler producers can add their own - just I think better use the first of the above alternatives, as then the code will also work in other C compilers not recognizing this pragma.
... I know that this might be quite an effort, as it concerns the very interior of the compiling/linking tables ... so just a polite question ... .
... sorry ... last message should say "I would NOT like to start from the scratch ...".
STL with lots of dynamic memory etc may not be a good choice.
And it may be a good idea to stay away from streams etc also, to keep down on size of linked libraries.
But C++ instead of C really doesn't matter much to a microcontroller as general as the ARM. You can write your programs as C programs with objects. Or C programs with namespaces. Or C programs with references. Or C programs with exceptions.
Good or bad experiences aren't really caused by the language, but how the user decides to use the language.
The main requirement for the processor is that it should have a full set of instructions for work through pointers, allowing good mapping of the "this" pointer that is a very important part of object-oriented C++ code.
So you would recommend to keep the assemply and C startup code from the basic example, and then start with the classes only in the main function and above?
I agree with you, that I anyway would not dare to include too much dynamic memory handling into the controller software.
So then I would mainly use the C++ classes in a sort of quasi-static approach (possibly even with most member functions static ...).
Just for now I think this is a bit too much for me, I have to think about it some time.
Anyway it would be nice, if Keil could present some simple C++ demo, maybe based on Blinky, to show the advantages and possible pitfalls of C++ concerning controller programming.
Classes are for C++ - not assembler.
So you will obviously not play around with any classes in the startup file.
You don't need static member methods. But you should think twice about how you allocate your objects. If they are global objects. Or created on the stack. Or from a special memory pool. Or from standard heap. Or if you are going to use something else.
What you have to realize is that the operator "new" isn't the only way to get object variables in C++.
That's what I meant with my statement "I would presumably use C++ in a sort of quasi-static approach".
If I skip new, then usually I would define all my classes global. And in this case of course it will not make much sense to use constructor / destructor functions. So the main advantage of using C++ then will restrict to the variable protection scheme of C++, which of course is very advanced.
... perhaps in some future I will try some small steps with some simple global C++ classes without constructor / destructor ...
an example using STL is located in:
C:\Keil\ARM\Examples\C++\Example1
another simple example using operator overloading and friend functions can be found in:
C:\Keil\ARM\Examples\C++\Example2
Constructors/destructors aren't bound to the use of "new" and "delete".
They apply just as well to global objects, or objects created on the stack.
You want to make classes complete - and that would include the use of constructors/destructors. Of course, some classes don't define anything that need destruction in which case you can get by with an empty default destructor.
But just as global C variables are always zeroed, you want all C++ objects (however they are created) to have a known state of all member attributes. Unless you think it's fun to debug programs having uninitialized variables taking random values depending on what was in memory before.