how does it happened that a variable used before it's declared?

I am confused about a function dictCreate() in file dict.c of redis implementation. I am going to paste the code here:

/* Create a new hash table 
 * T = O(1)
 */
dict *dictCreate(dictType *type, void *privDataPtr) {
    dict *d = zmalloc(sizeof(*d));
    _dictInit(d, type, privDataPtr);
    return d;
}

variable d is used in zmalloc(sizeof(*d)), but theoretically it will exist when this line was executed. So my question is how it is possible to use variable d before it is declared?

via Chebli Mohamed