C cast from specific function pointer to less specific function pointer

Question

Lets say I have the following code in C:

void general(void (*function)(void *something), void *something);
void funct_type1(struct something1 *something);
void funct_type2(struct something2 *something);
general(funct_type1, something1);
general(funct_type2, something2);

How do I compile this without pointer conversion warnings, and without manually suppressing some errors?

Later edit: I'm trying not to modify funct_type1() and func_type2() definition.

Answer 1

The proper fix is to fold the implementation-specific things into the function "behind" the abstract interface, ie:

void funct_type1(void *s1)
{
 struct something1 *s = s1;
 /* ... rest of function ... */
}

Otherwise you're going to have to cast the function pointer in the calls to general() .

Answer 2

You can use void *

void general(void (*function)(void *something), void *something);
void funct_type1(void* something);
void funct_type2(void* something);
general(funct_type1, &test1);
general(funct_type2, &test2);

where

void funct_type1(void* something)
{
   struct something1 *castedPointer = something;

//...YOUR STUFF
}

Or you can use an union to group your structs

#include <stdio.h>

struct something1
{
    int a;
};

struct something2
{
    int b;
};

union something3
{
    struct something1 s1;
    struct something2 s2;
};

void general(void (*function)(union something3 *something), union something3* something)
{
    if (function != NULL)
        function(something);
}

void funct_type1(union something3* something)
{
    something->s1.a = 1;

    printf("%s - something->s1.a = %d\n", __func__, something->s1.a);
}

void funct_type2(union something3* something)
{
    something->s2.b = 3;

    printf("%s - something->s2.b = %d\n", __func__, something->s2.b);
}

int main()
{
    union something3 test1;
    union something3 test2;

    test1.s1.a = 0;
    test2.s2.b = 0;

    general(funct_type1, &test1);
    general(funct_type2, &test2);

    printf("%s - test1.s1.a = %d\n", __func__, test1.s1.a);
    printf("%s - test2.s2.b = %d\n", __func__, test2.s2.b);

}