I have a small program that uses function pointers.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct _myst
{
    int a;
    char b[10];
}myst;

void cbfunc(myst *mt)
{
    fprintf(stdout,"called %d %s. \n",mt->a,mt->b);
}

int main()
{

    /* func pointer */
    void (*callback)(void *);

    myst m;
    m.a=10;
    strcpy(m.b,"123");

    /* point to callback function */
    callback = (void*)cbfunc;

    /* perform callback and pass in the param */
    callback(&m);

    return 0;

}
The function pointer decleration

void (*callback)(void*);
declares a function pointer callback that takes a generic-pointer and returns void.

While assigning cbfunc to callback

callback = cbfunc;
I get the warning

warning: assignment from incompatible pointer type [enabled by default]
If I use the following

callback = (void*)cbfunc;
It compiles without any warnings.I am using gcc (4.6.3) and compiling with CFLAGS=-g -O3 -Wall

Can someone explain the reason for this?