Pointer to a different function

[Gunslinger09]

Hi every one !

I need to create a linked list of pointers to different functions.
The question is: if i have pointer lets say void (*a)(int, int) how to assigen to it addres of void (*)(void). (I need to run this functions from pointers not just store an adress).



thanks. ;)

[Banfa]

If you need to run the function using the pointer then you will need a pointer to the right prototype when you try to invoke the function.

You can cast a point to function to a pointer to a differently prototyped function in the same way you can cast a pointer to float to a pointer to char.

[Gunslinger09]

Could you please show me exact sintance ?

[Banfa]

int mymax(int a, int b)
{
    return a>b?a:b;
}
 
int main()
{
    void (*pfn)(void);  /* Declare function pointer */
 
    pfn = (void (*)(void))mymax;  /* Assign location of mymax to function pointer  */
 
    /* But you can use pfn to call max with casting it back to the correct type */
 
    return 0;
}
 

[Gunslinger09]

Well this is your code, with small changes. But the function doesnt work from pfn pointer.

#include <iostream>

using namespace std;

int mymax(int a, int b)
{
return a>b?a:b;
}

int main()
{
void (*pfn)(void); /* Declare function pointer */

pfn = (void (*)(void))mymax; /* Assign location of mymax to function pointer */
// pfn = mymax;


pfn(1,2); // ERROR too many arguments to function


/* But you can use pfn to call max with casting it back to the correct type */

system("PAUSE");
return 0;
}

[Banfa]

It wouldn't, sorry I made a typo in my comment which should read

/* But you can't use pfn to call mymax with casting it back to the correct type */

((int (*)(int,int))pfn)(1,2);

[Gunslinger09]

ok....
but I can't see how it can help me...
that what iam trying to do->

typedef void (*voidFnPtr)();

voidFnPtr p=NULL;
voidFnPtr arrfunctions[10]={NULL}; //actually i need linked list but it only example.

// Also lets say i have function
int A(int) and
char B(void) //just 2 different functions.

then i need to do something like that =>
arrfunctions[0] = A
arrfunctions[1] = B

and be able to run it

arrfunctions[0]();
arrfunctions[1]();


can you help me?

[Banfa]

This is not possible, in order for the program to run correctly you MUST call the functions with the correct number of parameters.

You can not just store a list of pointers to void functions you have to preserve the function prototype to call them.

If you have a fixed number of function prototypes that may be in the llist then you could use a union of function pointers and an enum for each entry to indicate which is the correct one.

Just look at what you have already written

int A(int)

arrfunctions[0] = A;

arrfunctions[0]();

You would have called A that is expecting a int parameter with no parameters. This is undefined behaviour, anything might happen.

[Gunslinger09]

thanks man ;)

i had a hope that there is some way around it :) .but...

well now its all clear...