!memcmp in set

Good afternoon. I've already read the doc for memcmp still I don't understand why in this function:

Code:

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static int match_int(const void *key1, const void *key2) {

    /*****************************************************************************
    *                                                                            *
    *  Determine whether two integers match.                                    *
    *                                                                            *
    *****************************************************************************/

    return !memcmp(key1, key2, sizeof (int));

}

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memcmp has a logical negation operator instead of being written:

Code:

---

 
  return memcmp(key1, key2, sizeof(int));

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for a function of a set like this:

Code:

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int set_is_member(const Set *set, const void *data) {

    ListElmt *member;

    /*****************************************************************************
    *                                                                            *
    *  Determine if the data is a member of the set.                            *
    *                                                                            *
    *****************************************************************************/

    for (member = list_head(set); member != NULL; member = list_next(member)) {

        if (set->match(data, list_data(member)))
            return 1;

    }

    return 0;

}

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Quote:

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Originally Posted by thames

Good afternoon. I've already read the doc for memcmp still I don't understand why in this function:

Code:

---

    return !memcmp(key1, key2, sizeof (int));

---

---

memcmp returns 0 exactly when key1 and key2 are equal. Therefore !memcmp reverses the meaning, returning nonzero when they are equal. It is equivalent to writing

Code:

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bool is_equal = (memcmp(key1, key2, sizeof(int)) != 0);
return is_equal;

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Well memcmp returns 0 when both things match.

So the use of ! is to make the function return 1 (aka true) when things match, as opposed to 0.

You could also write with the same effect
return memcmp(key1, key2, sizeof (int)) == 0;