Re: [avr-gcc-list] calling function pointers via pointers ?

[Thomas Buchta]

On Wed, 28 Sep 2005 14:29:02 +0200, Lars Noschinski  
<address@hidden> wrote:

Hi Lars!

In many of my applications I use a called function pointer within an
array in program memory like such example code:

typedef INT8S (*PF_KEYFUNCTION) (MAIN_SYSTEM_STATE_T *ptrSystemState);

PF_KEYFUNCTION PROGMEM mainKeyFunction[N_MAX_KEYNUMBER][N_KEY_EVENTS] =
{
 /*    Key Event -> KEY_NOT_ACTIVE KEY_ACTIVE     KEY_LONG_ACTIVE  
KEY_VERY_LONG_ACTIVE KEY_RELEASED  */
 /* Key        */
 /*   0 KEY_02 */ { no_function,   mixMatrixNode, gainDelaySet,    
no_function,         mixMatrixNode_update_req,  },
...
 /*  31 KEY_31 */ { no_function,   mixMatrixNode, gainDelaySet,    
no_function,         mixMatrixNode_update_req,  }
};

void foo(void)
{
  INT8S (*ptrF_KeyFunction) (MAIN_SYSTEM_STATE_T *ptrSystemState);

  ....

  /* get copy of function pointer       */
  memcpy_P((void*)&ptrF_KeyFunction,
           (PGM_VOID_P)&mainKeyFunction[keyNumber][action],
           2
          );

  /* call the function                  */
  ptrF_KeyFunction (ptrMSystemState);

  ...

}


> * Vincent Trouilliez <address@hidden> [2005-09-28  
> 14:16]:
> > Another pointer problem again, oops...
> > I need pointers to functions in my project. Using the great on-line
> > resource http://www.eskimo.com/~scs/C-faq/q4.12.html which someone on
> > here mentioned recently, I got the basics working.
> > But my actual case at hand is a bit trickier and I am lost again (okay,
> > doesn't take much to loose myself I admit ;-).
> >
> > Problem: my function pointers are in an array, within a structure, which
> > itself is accessed via pointers... oh dear.
>
> Just do it step by step, at least for first tries use temporary
> variables - you can avoid those after you understood what to do ;)
>
> - Dereference the pointer to the struct. This gives you a struct.
> - Select the field from the struct. This gives you an array.
> - Select the entry from the array. This gives you a function pointer.
> - Dereference the function pointer and call the function.
>
> Done.
>
>
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