C - Take and return pointer to function

Author

Take and return pointer to function

Frederick Gotham

2006-06-29, 6:56 pm

lovecreatesbeauty posted:

> A more complex example with function pointers is the function:
>
> #include <signal.h>
> void (*signal(int sig, void (*func)(int)))(int);

I like the hardcore method ; )

/* Hardcore method */

void (*signal_hardcore(int, void (*p)(int)))(int)
{
return p;
}

/* Dumbed-down method */

typedef void (*Ptr_FuncTakeIntReturnVoid)(int);

Ptr_FuncTakeIntReturnVoid signal_dumb( int, Ptr_FuncTakeIntReturnVoid p )
{
return p;
}

/* Both used the same way */

void Func(int) {}

int main(void)
{
signal_dumb( 0, Func );

signal_hardcore( 0, Func );
}

--

Frederick Gotham

Frederick Gotham

2006-06-29, 6:56 pm

Frederick Gotham posted:

> I like the hardcore method ; )

Who's up for role play? I have an idea for a game!

You've to come up with as complicated a function signature as you can,
but... you also have to devise a story in order to justify its complexity.

OK I'm first!

How about some sort of "runtime-programmable calculator".

All of its operations can be performed using simple functions which all
have the same signature, e.g.:

int Add(int,int);
int Subtract(int,int);
int Divide(int,int);

The calculator must be supplied at runtime with 16 such functions.

The programmable calculator queries a database looking for these 16
operations, and receives a pointer to a 16-element-array of pointers to
functions. (It returns a pointer to an array of definite size rather than a
pointer to the first element of an arrary in order to emphasize that the
array's length must be 16.). Furthermore, in the same query, you must
supply the database with a callback function which it should invoke before
and after it goes checking the database, to indicate its current status.
The callback funtion should have the following signature:

void Indicate(int);

Okay here's what I've got:

/* Let's start off with an actual function */

#include <stdio.h>

int Addition(int const a, int const b)
{
int result = a + b;

printf( "The addition of %i and %i yields: %i\n", a, b, result );

return result;
}

/* Here's the callback function which gets invoked to
inform us of the database's current status. */

void Indicate(int) {}

/* Here's the function which accesses the database and retrieves
our mathematical operations as pointers to functions. */

int (*(*RetrieveOperations(void(*pCallback)(
int)))[16])(int,int)
{
pCallback(0);

static int (*array[16])(int,int) =
{ Addition, Addition, Addition, Addition, Addition, Addition,
Addition, Addition, Addition, Addition, Addition, Addition,
Addition, Addition, Addition, Addition };

pCallback(1);

return &array;
}

int main(void)
{
int (*(*p_array)[16])(int,int) = RetrieveOperations(Indicate);

/* Now let's call a few functions */

(*p_array)[0](1,2);
(*p_array)[4](3,4);
(*p_array)[9](5,6);
(*p_array)[12](7,8);
}

Looking forward to reading others' contributions : )

--

Frederick Gotham

Kenneth Brody

2006-06-29, 6:56 pm

Frederick Gotham wrote:
>
> Frederick Gotham posted:
>
>
> Who's up for role play? I have an idea for a game!
>
> You've to come up with as complicated a function signature as you can,
> but... you also have to devise a story in order to justify its complexity.
>
> OK I'm first!
>
> How about some sort of "runtime-programmable calculator".
[...]
> int (*(*RetrieveOperations(void(*pCallback)(
int)))[16])(int,int)
[...]

You forgot to mention that there are 4 modes of this calculator,
and therefore it needs to return an array of 4 pointers to these
16-element arrays.

Ready... Go!

Is it possible to declare a function which returns a struct*, with
the struct definition within the prototype?

For example, rather than the 16-element array of pointers to your
handler functions, each array element is a struct consisting of a
pointer to an int version of the function, and to a double version
of the function.

--
+-------------------------+--------------------+-----------------------+
| Kenneth J. Brody | www.hvcomputer.com | #include |
| kenbrody/at\spamcop.net | www.fptech.com | <std_disclaimer.h> |
+-------------------------+--------------------+-----------------------+
Don't e-mail me at: <mailto:ThisIsASpamTrap@gmail.com>

Frederick Gotham

2006-06-29, 6:56 pm

Kenneth Brody posted:

> [...]
> [...]
>
> You forgot to mention that there are 4 modes of this calculator,
> and therefore it needs to return an array of 4 pointers to these
> 16-element arrays.

Of course, how negligent of me! Please accept my sincerest apologies.
Here's the updated code as requested ; )

/* Let's start off with an actual function */

#include <stdio.h>

int Addition(int const a, int const b)
{
int result = a + b;

printf( "The addition of %i and %i yields: %i\n", a, b, result );

return result;
}

/* Here's the callback function which gets invoked to
inform us of the database's current status. */

void Indicate(int) {}

/* Here's the function which accesses the database and retrieves
our mathematical operations as pointers to functions. */

int (*(*RetrieveOperations(void(*pCallback)(
int)))[16])(int,int)
{
pCallback(0);

static int (*array[16])(int,int) =
{ Addition, Addition, Addition, Addition, Addition, Addition,
Addition, Addition, Addition, Addition, Addition, Addition,
Addition, Addition, Addition, Addition };

pCallback(1);

return &array;
}

/* Here's the function which retrieves four modes. */

int (*(*(*RetrieveFourModes(void(*pCallback)
(int)))[4])[16])(int,int)
{
static int (*(*array[4])[16])(int,int);

*array = RetrieveOperations( Indicate );
array[1] = RetrieveOperations( Indicate );
array[2] = RetrieveOperations( Indicate );
array[3] = RetrieveOperations( Indicate );

return &array;
}

int main(void)
{
int (*(*(*p_array)[4])[16])(int,int) = RetrieveFourModes(Indicate);

/* Now let's call a few functions */

(*((*p_array)[0]))[15](1,2);
(*((*p_array)[1]))[14](7,3);
(*((*p_array)[2]))[13](55,8);
(*((*p_array)[3]))[12](1045,87);
}

--

Frederick Gotham

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