Thread: Handling of callback function that is not registered

I have a problem of how to handle registering of a callback function.

In Example 1, I commented away reg_cb(f1); and in the function irq_handler() the check is working ok (callback = NULL).

However in the second example, Example 2 where the callback function is an element in a struct, the handling is a bit strange. If I comment away bp->func = f1; it looks like the check does not realize the element is NULL.

I don't realise what is going on. Can anyone explain this please?

Regards

Example 1

Code:

#include <stdio.h>
#include <stdlib.h>
 
void f1()
{
        printf("%s() -\n", __func__);
}

void (*callback)(void);
void reg_cb(void(*cb)(void))
{
        printf("%s() -\n", __func__);
        callback = cb;
}
 
void irq_handler(void)
{
    printf("%s() -\n", __func__);
    if (callback != NULL)
    {
            callback();
    }
    else
    {
            printf("cb not registered\n");
    }
}
 
int main(int argc, char *argv[])
{
    reg_cb(f1);
    irq_handler();

    return 0;
}

Example 2

Code:

#include <stdio.h>
#include <stdlib.h>
 
void f1()
{
        printf("%s() -\n", __func__);
}
 
struct block
{
    int var;
    void (*func)(void);
};


int main(int argc, char *argv[])
{
    struct block *bp;
    struct block b;

    bp = &b;
    bp->var = 10;
    bp->func = f1;

    printf("var=%d\n", bp->var);

    if (bp->func) 
    {
           bp->func();
    }
    else
    {
           printf("Not registered\n");
    }

    return 0;
}