easy pointers to functions problem

[Michael]

Hi,

I am trying to get an idea of how function pointers work.
I have the following:

#include <stdio.h>

void do_stuff(int*,i nt,void*);
void getInt(int*);
void showInt(int*);

int main(){

int num_array[10];

do_stuff(num_ar ray, 10, getInt);
do_stuff(num_ar ray, 10, showInt);

return(0);
}

void do_stuff(int *a, int size, void (*process)(int *)){
int i;
for(i = 0; i < size; i++){
process(&a[i]);
}
}

void getInt(int *ptr){
if((scanf("%d", ptr)) != 1){
printf("error") ;

}
}

void showInt(int *ptr){
printf("%d", *ptr);
}

but I get errors "conficting types for do_stuff" and also warnings "ISO C
forbids passing of arg3 of do_stuff between pointer and void *"

I'm getting nowhere fast here. Can someone help me out with what I have
wrong?

Thanks

Michael

[Herbert Rosenau]

On Thu, 27 Jul 2006 06:13:14 UTC, "Michael" <mi*********@ya hoo.com>
wrote:

Hi,

I am trying to get an idea of how function pointers work.
I have the following:

#include <stdio.h>

void do_stuff(int*,i nt,void*);

No, you means

void do_stuff(int *a, int size, void (*process)(int *));

as the 3th parameter is truly not a pointer to void but to a function
returning voind and getting a single parameter of type pointer to
void. You have to declare the prototype always like a function
definition - but without the definition itself.

void getInt(int*);

Better selfdocumenting :
void getInt(int *ptr);

void showInt(int*);

and
void showInt(int *ptr);

Ther compiler will still ignore the name of the parameter in a
prototype but the reader will assign some description with it when the
name of the parameter does describe it.

int main(){

int num_array[10];

do_stuff(num_ar ray, 10, getInt);
do_stuff(num_ar ray, 10, showInt);

return(0);
}

void do_stuff(int *a, int size, void (*process)(int *)){
int i;
for(i = 0; i < size; i++){
process(&a[i]);
}
}

void getInt(int *ptr){
if((scanf("%d", ptr)) != 1){
printf("error") ;

}
}

void showInt(int *ptr){
printf("%d", *ptr);
}

but I get errors "conficting types for do_stuff" and also warnings "ISO C
forbids passing of arg3 of do_stuff between pointer and void *"

I'm getting nowhere fast here. Can someone help me out with what I have
wrong?

Thanks

Michael

--
Tschau/Bye
Herbert

Visit http://www.ecomstation.de the home of german eComStation
eComStation 1.2 Deutsch ist da!

[Dave Thompson]

On 28 Jul 2006 16:42:43 GMT, mw*****@newsguy .com (Michael Wojcik)
wrote:

>
In article <11************ *********@m79g2 000cwm.googlegr oups.com>, "lovecreatesbea uty" <lo************ ***@gmail.comwr ites:

I think typedef is unuseful totally.

There is at least situation where it is the only solution: for
using certain types with the va_arg macro. va_arg requires that
if used with type T, as in va_arg(ap, T), that T* be a pointer
to an object of type T.

This doesn't work with function pointers. <snip>

Also "true" array pointers, that is with actual type pointer to array
instead of the normal convention of pointer to (first) element.
Although it is arguable these are less common -- and certainly less
vital -- than function pointers.

The syntax also doesn't work for function types and array types --
int (double) * and int [5] * are syntactically invalid -- but as those
types can never be arguments (var or not) anyway, the inability to
fetch them with va_arg becomes of distinctly lesser importance.

- David.Thompson1 at worldnet.att.ne t