passing function with variable parameter as void pointer, and calling it

Question

I have a function which I want to pass through various functions

int func1(char *ptr)
{
    printf("%s",ptr);
    return 0;
}

and other function in which I want to call the func1

int func2(void *i)
{
    //call i
    //here i point to function func1
    //and do something with return value of i
}

So, how should I call it in main()?

int main()
{
    void *d;
    //SOMETHING wrong in next four line
    d=&func1("abcd");
    func2(d);
    d=&func1("xyz");
    func2(d);
    return 0;
}

Answer 1

You can simply create a function (func2) that takes a function pointer to your desired function that you want called and another paramter that takes a pointer to your string. Then in func2 call the passed in function pointer with the str argument.

#include <stdio.h>

void func1(const char *str)
{
    puts(str);
}

void func2(void (*fp)(const char *), const char *str)
{
    fp(str);
}

int main(void)
{
    const char *str = "Hello world.";

    func2(func1, str);

    return 0;
}

Answer 2

First of all: A function pointer refers to a function only. Parameters come into the game when the function is called, either directly or via a function pointer.

So if you want to achieve what you have in mind, that is binding a (set of) parameters to a specific function varaible you need to use a wrapper function:

int func1(char * pc)
{
  int i;
  /* assigne somehting to "i" and use "pc" */
  return i;
}

int func1_abcd(void)
{
  return func1("abcd")
}

int func1_xyz(void)
{
  return func1("xyz")
}

typedef int (*pfunc1_wrapper_t)(void);

int func2(pfunc1_wrapper_t pfunc1_wrapper)
{
  return pfunc1_wrapper();
}

int main(int argc, char ** argv)
{
  pfunc1_wrapper_t pfunc1_wrapper = NULL;
  int i = 0;

  pfunc1_wrapper = func1_abcd;
  i = func2(pfunc1_wrapper);

  pfunc1_wrapper = func1_xyz;
  i = func2(pfunc1_wrapper);

  ...

  return 0;
}

Answer 3

You should first of all use Function pointers to do the job you desire. Using void pointer is a method where you before hand know what you will cast it to for dereferencing. Since you are passing the address of a function, you should cast it to a function pointer anyways. So avoid all this and declare func pointer anyways. Use void * only if you know that you can handle all the possiblities. eg. memcpy uses void * this is acceptable as you just want a bunch of data in soure location to be copied to a destination location.

#include <stdio.h>
void func1(char * str)
{
   printf("%s",str);
}
void func2(void * g)
{
   void (*p) (char *);   //function pointer
   p = (void (*)(char *))g;//casting void * to pi.e func pointer reqiuired eitherways.
   p("Func pointer caller");
}
void main()
{
   void * d = func1; // name of the function is itselt its address
   //printf("func1 = %d\nd = %d",func1,d);  
   func2(d);
}

all this can be avoided by a simple function pointer.