Re: Take and return pointer to function

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
.

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