"PORTING C" > Function Pointers issue.
Robby
I give up! This used to work! Now I get errors.
I have looked at it all afternoon and tried everything forwards and backwards!
I haven't used function pointers for quite a while, but all of this compiled
back then.
So again, I watered down code. I don't get it, the pointer to functions
declaration is typedefed after all the typedefed structures. And the arrays
of function pointers is declared right after that. And then I declared the
function prototype right after that.
Here are the errors I get:
c(1) : error C2061: syntax error : identifier 'CALLBACK_WP_INTRO'
1>c:\_dts_programming\pic\_microchip_issues\vc++\function_pointers\function_pointers\wp_intro.c(1) : error C2059: syntax error : ';'
1>c:\_dts_programming\pic\_microchip_issues\vc++\function_pointers\function_pointers\wp_intro.c(1)
: error C2146: syntax error : missing ')' before identifier 'hwnd'
1>c:\_dts_programming\pic\_microchip_issues\vc++\function_pointers\function_pointers\wp_intro.c(1) : error C2061: syntax error : identifier 'hwnd'
1>c:\_dts_programming\pic\_microchip_issues\vc++\function_pointers\function_pointers\wp_intro.c(1) : error C2059: syntax error : ','
1>c:\_dts_programming\pic\_microchip_issues\vc++\function_pointers\function_pointers\wp_intro.c(1) : error C2059: syntax error : ')'
Here is the code:
===============KERNEL.h
typedef long *LRESULT;
typedef long WPARAM;
typedef long LPARAM;
typedef struct tagHwnd {
long caption_msg;
} HWND;
typedef struct tagMsg {
HWND hwnd;
long msg;
WPARAM wParam;
LPARAM lParam;
long time;
} KM_MSG;
// Pointer to function declaration (Used for callbacks!)
typedef LRESULT(*callBack)(HWND hwnd, long message, WPARAM w, LPARAM l);
callBack cb[1]; // Array of function pointers
// Function declaration!
LRESULT CALLBACK_WP_INTRO(HWND hwnd, long message, WPARAM wParam, LPARAM
lParam);
===============KERNEL.c
#include <stdio.h>
#include "KERNEL.h"
int main(void)
{
KM_MSG m;
HWND hwnd;
hwnd.caption_msg = 1;
m.msg = 1;
m.lParam = 2;
m.wParam = 3;
cb[0] = CALLBACK_WP_INTRO;
CALLBACK_WP_INTRO(hwnd, m.msg, m.wParam, m.lParam);
}
===============WP_INTRO.c
LRESULT CALLBACK_WP_INTRO(HWND hwnd, long message, WPARAM wParam, LPARAM
lParam)
{return 0; }
==========================
But if I do this, it compiles without errors ??
===============KERNEL.h
typedef long *LRESULT;
typedef long WPARAM;
typedef long LPARAM;
typedef struct tagHwnd {
long caption_msg;
} HWND;
typedef struct tagMsg {
HWND hwnd;
long msg;
WPARAM wParam;
LPARAM lParam;
long time;
} KM_MSG;
// Pointer to function declaration (Used for callbacks!)
typedef LRESULT(*callBack)(HWND hwnd, long message, WPARAM w, LPARAM l);
callBack cb[1]; // Array of function pointers
// Function declaration!
LRESULT CALLBACK_WP_INTRO(HWND hwnd, long message, WPARAM wParam, LPARAM
lParam);
===============KERNEL.c
#include <stdio.h>
#include "KERNEL.h"
LRESULT CALLBACK_WP_INTRO(HWND hwnd, long message, WPARAM wParam, LPARAM
lParam)
{return 0; }
int main(void)
{
KM_MSG m;
HWND hwnd;
hwnd.caption_msg = 1;
m.msg = 1;
m.lParam = 2;
m.wParam = 3;
cb[0] = CALLBACK_WP_INTRO;
CALLBACK_WP_INTRO(hwnd, m.msg, m.wParam, m.lParam);
}
==========================
All help sincerely appreciated!!
Robert
Igor Tandetnik
> ===============KERNEL.h
> // Pointer to function declaration (Used for callbacks!)
> typedef LRESULT(*callBack)(HWND hwnd, long message, WPARAM w, LPARAM
> l);
>
> callBack cb[1]; // Array of function pointers
Don't define variables in headers.
> ===============WP_INTRO.c
> LRESULT CALLBACK_WP_INTRO(HWND hwnd, long message, WPARAM wParam,
> LPARAM
> lParam)
> {return 0; }
Since you haven't included KERNEL.h here, the compiler doesn't know what LRESULT or HWND or WPARAM or LPARAM are.
> But if I do this, it compiles without errors ??
> ===============KERNEL.c
> #include <stdio.h>
> #include "KERNEL.h"
>
> LRESULT CALLBACK_WP_INTRO(HWND hwnd, long message, WPARAM wParam,
> LPARAM
> lParam)
> {return 0; }
Here you did include KERNEL.h, so the compiler does know what LRESULT or HWND or WPARAM or LPARAM are.
--
With best wishes,
Igor Tandetnik
With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead. -- RFC 1925
Robby
Darn global stuff, gets me everytime! :-)
"Igor Tandetnik" wrote:
> Robby <Ro...@discussions.microsoft.com> wrote:
> > ===============KERNEL.h
> > // Pointer to function declaration (Used for callbacks!)
> > typedef LRESULT(*callBack)(HWND hwnd, long message, WPARAM w, LPARAM
> > l);
> >
> > callBack cb[1]; // Array of function pointers
>
> Don't define variables in headers.
Sincerely Igor, I don't see how the language treats "callback cb[1];" as a
variable definition? But then what do I know... right!
Isn't:
callBack cb[1];
a "declaration" of an array holding 1 function pointer of type callback ???
I don't see where I defined anything here? I mean I didn't do something like
this:
cb[0] = CALLBACK_WP_INTRO;
Which would imply that I **defined/assigned** something to the array !!!!
And also:
Isn't:
int x;
a variable *declaration* and shouldn't,
int x = 2;
be considered as a variable *definition*, because the latter is defining
what x is to be which is 2 ? The former instead just declares x.
Please do get get back, I would like to iron out these simple vexatious
details once and for all.
> > ===============WP_INTRO.c
> > LRESULT CALLBACK_WP_INTRO(HWND hwnd, long message, WPARAM wParam,
> > LPARAM
> > lParam)
> > {return 0; }
>
> Since you haven't included KERNEL.h here, the compiler doesn't know what LRESULT or HWND or WPARAM or LPARAM are.
Okay, understood! I'll get used to it!
> > But if I do this, it compiles without errors ??
> > ===============KERNEL.c
> > #include <stdio.h>
> > #include "KERNEL.h"
> >
> > LRESULT CALLBACK_WP_INTRO(HWND hwnd, long message, WPARAM wParam,
> > LPARAM
> > lParam)
> > {return 0; }
>
> Here you did include KERNEL.h, so the compiler does know what LRESULT or HWND or WPARAM or LPARAM are.
Understood.
Thankyou for helping me!
Regards
Rob
Igor Tandetnik
> Isn't:
>
> callBack cb[1];
>
> a "declaration" of an array holding 1 function pointer of type callback ???
No, it's a definition (well, formally, it's a declaration that is also a definition). A declaration would look like this:
extern callback cb[1];
> I don't see where I defined anything here? I mean I didn't do something like
> this:
>
> cb[0] = CALLBACK_WP_INTRO;
This is neither a declaration nor a definition. It's a statement. It doesn't introduce a new name, nor cause storage to be allocated.
> Which would imply that I **defined/assigned** something to the array !!!!
Definition and assignment are two entirely different, largely unrelated things. You can define a variable only once in the program, but you can assign a new value to it multiple times.
> Isn't:
>
> int x;
>
> a variable *declaration* and shouldn't,
>
> int x = 2;
>
> be considered as a variable *definition*
Both are definitions, one with an initializer and one without (and thus implicitly initialized to 0, assuming it's a global variable).
> because the latter is defining
> what x is to be which is 2 ?
Not defining - initializing. Again, when defining a global variable, "int x;" is equivalent to "int x = 0;". On the other hand, this would be a declaration:
extern int x;
Robby
On another note, I was browsing for some function pointer samples on the
Internet and I came across a sample at:
http://stackoverflow.com/questions/252748/how-to-use-array-of-function-pointers
Its the 2nd sample that concerns me which looks like this:
========================================
void fun1()
{
}
void fun2()
{
}
void fun3()
{
}
void (*func_ptr[3]) = {fun1, fun2, fun3};
main()
{
int option;
printf("\nEnter function number u want");
printf("\nyou should not enter other than 0 , 1, 2"); /*bcos we hav only 3
functions*/
scanf("%d",&option);
if((option>=0)&&(option<=2))
{
(*func_ptr[option])();
}
return 0;
}
==================================
Does this compile at your end... cause I get errors on this sample.
The reason I ask also is that I was wondering if we can really initialize an
array of pointers all in one line like they did at the following line:
void (*func_ptr[3]) = {fun1, fun2, fun3};
For me it seems weird ! shouldn't it of been:
void (*func_ptr[3]) (...parameter list...) ;
Asides from the lack of inclusions there is an error that points to the
following line:
(*func_ptr[option])();
here's the error:
c:\_dts_code_testing\_testing_personal_samples\function_pointers\function_pointers\t.c(29) : error C2100: illegal indirection
Thanks for your help.
--
Best regards
Roberto
Igor Tandetnik
> On another note, I was browsing for some function pointer samples on the
> Internet and I came across a sample at:
>
> http://stackoverflow.com/questions/252748/how-to-use-array-of-function-pointers
>
It's a typo. It's supposed to be
void (*func_ptr[3])() = {fun1, fun2, fun3};
Note an extra pair of parentheses.
Barry Schwarz
<itand...@mvps.org> wrote:
>Robby wrote:
>> On another note, I was browsing for some function pointer samples on the
>> Internet and I came across a sample at:
>>
>> http://stackoverflow.com/questions/252748/how-to-use-array-of-function-pointers
>>
>> void (*func_ptr[3]) = {fun1, fun2, fun3};
>
>It's a typo. It's supposed to be
>
>void (*func_ptr[3])() = {fun1, fun2, fun3};
>
>Note an extra pair of parentheses.
It's amazing that he found this brain dead example among all the
correct ones (at least syntactically) that google displays.
--
Remove del for email
Robby
> Robby wrote:
> > On another note, I was browsing for some function pointer samples on the
> > Internet and I came across a sample at:
> >
> > http://stackoverflow.com/questions/252748/how-to-use-array-of-function-pointers
> >
> > void (*func_ptr[3]) = {fun1, fun2, fun3};
>
> It's a typo. It's supposed to be
>
> void (*func_ptr[3])() = {fun1, fun2, fun3};
>
> Note an extra pair of parentheses.
Thanks Igor.
Rob