取消引用时，转换为字符指针的 void 指针会崩溃

Question

I'm trying to implement DJB algorithim in C to build a dictionary like structure.

My implementation works well if the key passed is a char pointer however if i pass for example a integer it crashes, I'm not sure why and how could i accomplish this. Basically I'd need to hash both a string and a integer.

static unsigned int DJBHash(void* key, unsigned int len) {
    unsigned int hash = 5381;
    unsigned int i = 0;
    char* ptr = (char *)key;

    for (i = 0; i < len; i++)
    {   
        hash += hash << 5;
        hash += *ptr;         /* crashes if key is not originally a char* */
        ptr++;
    }   

    return hash;
}

this get simply called to get an hash value: DJBHash((void*)420, sizeof(420)); crashses while DJB((void*)"foo", sizeof("foo")); works perfectly fine.

Answer 1

DJBHash(420, sizeof(420)); crashses while DJB("foo", sizeof("foo")); works perfectly fine.

That's because using 420 isn't a valid memory address in your program. So when your function tries to use that memory address it crashes. Normally you wouldn't even try to force a specific memory address in this fashion. It only works in very specific cases like when its a known address in kernel space or something like that.

If you want to hash an integer instead of specific memory location it would be:

int j = 420;
DJBHash(&j, sizeof(j));