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By not working, do you mean it doesn't compile, doesn't show the values you thought, or someting other?
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It will not compile using msvc++ 2015
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Member 9411471 wrote: It will not compile using msvc++ 2015
And what compiler error does it produce?
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CString weekday[] = {CString ("Sun"), CString( "Mon")...};
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OK, this is really simple question, with example code to boot.
The function pointer declaration is this
void (*gpf_isr)(void) = (0UL);
It is used by this function
void UOTGHS_Handler( void )
{
if (gpf_isr)
gpf_isr();
}
and I access it like so
extern void (*gpf_isr)(void);
then I assign my local poiter / version of the function
gpf_isr = ( object ) . UTOGHS_Handler;
The silly question why this also get pass the compiler , no errors
extern void (*gpf_isr)(void) = (0UL);
The pointer gets reassigned , but ...
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That is pretty clear that defining the variable is OK, but if optioned GCC will give a warning.
Kind like deleting a file and being ask "are you sure?"
Thanks
.
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Yes. You may find (on the web) folks arguing that warning is not legitimate.
In a clean implementation you don't qualify with extern the variable in the source file wherein you define it.
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The key point here is the extern qualifier. That states that the variable can be referred to from any module in the final linked executable, but only one instance of it will actually exist.
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C++ has very specific way / syntax to instantiate a class with parameters,
so basic that Google can't find it for me .
I need this for implementing multiple inheritance.
I can instantiate the "top class" in multiple inheritance hierarchy , but it uses system generated default constructors, without parameters of course.
My goal is to create an instance of the top class with parameters passed to the hierarchy lower chain classes.
Do I make sense? I hope so.
Thanks
Vaclav
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Quote: but it uses system generated default constructors, without parameters of course Only if you don't provide an implementation of (with or without parameters) the class contructor.
Quote: My goal is to create an instance of the top class with parameters passed to the hierarchy lower chain classes.
Do I make sense? Before attempting the multiple-inheritance step, make sure you understand how class constructor/destructor work.
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class A
{
public :
A( int p ) : a( p )
{
}
protected:
int a;
};
class B
{
public:
B( int q ) : b( q )
{
}
protected:
int b;
};
class C : public A, B
{
public :
C( int x, int y, int z ) : A( x ), B( y), c( z )
{
a = x;
}
private:
int c;
};
int _tmain(int argc, _TCHAR* argv[])
{
C test( 1, 2, 3 );
return 0;
}
Will this help?
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Well, it does and does not help.
I am probably wrong , but I was looking for something like this
class TestClass : paramaterX = "Text"
{
}
I am looking into multiple inheritance and was trying to verify that the classes in the scheme were actually constructed.
Simple
class A : public B,C,D
setup.
So I implemented default constructor and have it to output some text to the console, sort of. It does work.
Now I am trying to find a way to instantiate the scheme with parameters passed to some of the hierarchy classes.
something like
class A : ( class A parameter list ), public B : ( class b parameter list)...
Is that possible ?
BTW I cannot figure out the real syntax / usage of the basic syntax
class A : ?
For example
class A : text
{
};
the compiler wants to see class definition before "text", text is class A variable.
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You could be trying to do several things with the multiple inheritance you need to be very precise here.
You give us "parameterX" which is sort of labelled as text but that could mean a string class, a c string,
or a static const array. You also don't tell us whether the place you want to store the passed text is
in the object new to this class or part of one of the inherited classes, it may matter .. depends.
Do you see how many variations there are on what your simple description says? This is what makes multiple
inheritance tricky and you need to be very clear.
If you search the words "C++ composite class" is that what you are trying to do?
It appears to me you have jumped in at the deep end with C++ classes and trying to do the most complex
without first understanding the basics. I would highly recommend you might like to also do a search of
"C++ Parameterized Constructor" and review it given the code you have written above is nonsense.
I would also recommend you look at
Constructors (C++)[^]
That covers the basics of construction order and explicit and derived constructors in multiple inheritance.
My best guess you are trying to derive the base of a composite class and it would be this
class TestClass {
public:
TestClass(const string& InitText) { text = InitText; };
string text;
};
In vino veritas
modified 3-Oct-16 23:05pm.
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Hi,
Vaclav_Sal wrote: something like class A : ( class A parameter list ), public B : ( class b parameter list)...Is that possible ?
As a direct answer, I would say that, it is not possible and instead, we can use constructors with parameters.
Vaclav_Sal wrote: BTW I cannot figure out the real syntax / usage of the basic syntax class A : ? For example class A : text{};
Please have a look at Richard's link too.
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I just twigged what he is trying to do via you answer, he is trying to make a static composite class isn't he.
Like when beginners to C, try to create a struct with constants within the struct definition.
In vino veritas
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Let me try it again.
I have an inheritance hierarchy
class A : public B, C
When I instantiate class A - A a; - all classes get constructed via default constructor provided by the language if I do not specify them.
Now this is not much over my head , I don't see need to further educate myself in this basic.
This inheritance scheme at that point works just fine.
Next step - class B needs to be constructed using real constructor. Again I know how to pass parameters to class constructor.
<b>I just do not know how to do it , or can it be done during the construction of the class A.
</b>
As far as taking on more than I can chew, that's my business.
If you do not want to participate, that is your choice.
No "google it" remarks are worthy of your and my time.
I am sorry about the above remarks , but I am getting tired of folks with " my grandma can beat up yours " attitude. I just hate to see it popping up on this forum too.
All I actually need to know is "composite class", and I can take it from there.
Thanks
-- modified 4-Oct-16 9:26am.
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Vaclav_Sal wrote: I am getting tired of folks with " my grandma can beat up yours " attitude. Much as we feel about you.
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Sorry my mind reading was a bit off, I am however glad you worked out you were trying to build a composite class.
The forum can help with specific small problems but it's not something that can teach complex techniques in C++.
In vino veritas
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Yes, this time using correct terminology was the ticket. I am not sure why the OP was judged as too complex to ask here about. I am still puzzled why I did not get a clear example of syntax passing list of parameters to class directly, not via constructor. The link posted was not that clear how to name / use the list.
It really does matter to me how I get the parameters to correct class in the hierarchy.
The example of composite class suggest I have to follow the hierarchy and pass the parameters thru each constructor to the next one.
I suppose when I get the code to play I could post it here for everybody can see it is really not that complex.
Cheers
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Correct
The problem as you will find is hierarchy order as you will find. Sometimes the order will not
be the way you want in different functions and you will need to control it and that gets down
to some very nitty details.
The question we will still always pose back to you is do you really need the hierarchy at all.
I can't stress enough to read one article from wikipedia it can save you alot of heartache
https://en.wikipedia.org/wiki/Composition_over_inheritance[^]
In vino veritas
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I am writing standard C programming language for an ARM processor and I would like to combine a handle (a pointer to a struct with state variables) with an enum like this:
struct MyStateStruct_t {
int a;
};
const struct MyStateStruct_t myStates [2];
typedef enum
{
MY_SELECTOR_0 = (const int)(&myStates[0]),
MY_SELECTOR_1 = (const int)(&myStates[1])
} MyEnum_e;
When I try to compile, I get the following errors:
enumerator value for 'MY_SELECTOR_0' is not an integer constant
enumerator value for 'MY_SELECTOR_1' is not an integer constant
Does anybody know a workaround? Of course, I could use a look-up table array to convert from the enum-values to the addresses, but if possible I would like to avoid that. Thanks for any help!
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Enums must be defined integer constants at compile time.
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As Richard said enum is
1.) Restricted to a 16 bit integer constant
2.) Must be defined at compile time
Your pointer is longer than 16 bits and the address is only available at runtime, so it double fails.
You also haven't typedef the structure to a name.
I suspect this is what you are trying to do
typedef struct MyStateStruct_t {
int a;
} MYSTATE;
typedef enum {
MY_SELECTOR_0 = 0,
MY_SELECTOR_1 = 1
} MyEnum_e;
const MYSTATE myStates[2];
enum MyEnum_e selector = MY_SELECTOR_0;
int result1 = myStates[selector].a;
selector = MY_SELECTOR_1;
int result2 = myStates[selector].a;
In vino veritas
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