Question

A little context: I’m trying to make a very simple hashing function/hash table as described here. I’m basically on the first step, blindly adding a key to an array based on the letter it starts with (no checking if space is occupied yet). The code I’m using to do this so far:

int main(int argc, char **argv) {
    char *arrayKeys[300];
    std::string aName("Charles");

    char *aNameCpy = new char[aName.size() + 1];
    std::copy(aName.begin(), aName.end(), aNameCpy);
    aNameCpy[aName.size()] = '\0';

    int kPos = storeKey(arrayKeys, aNameCpy);

    std::cout << "The new position in arrayKeys for 'Charles' is:  " <<
        kPos << "\ncontaining the text: " << arrayKeys[kPos] << std::endl;
    delete[] aNameCpy;  
    return 0;
}

int storeKey(char **keys, char *key) {

    int charLett = -1;
    charLett = (int)key[0];
    if(charLett != -1)
        charLett = charLett - 65;

    keys[charLett * 10] = key;

    return charLett*10;
}

My question is, how can I add a string to the array (arrayKeys) where it is fully apart of the array, and not reliant upon the original string? If I delete the copy of the string (aNamCpy) before I print the array key out, the array key turns into garbled symbols. I’m copying the string before sending it to the function because I need a non-const string to add to the arrayKeys array (so it can be modified), and any method of string I looked at seemed to return const.

(Another version of this I attempted can be found here, but I would rather not initialize the arrayKeys like that – with a definite second dimension (string) length)
C++ is still very new to me so I can’t figure out how to juggle the non-const part with copying the string into arrayKeys. Any help would be very much appreciated.

Answer 1

Here’s how I’d change the code to use more modern C++ constructs. I think you’ll find this way easier to use.

int storeKey(vector<string> &keys, const string &key) {
    int charLett = -1;

    if (!key.empty()) {  // you weren't doing this before!
        charLett = key[0];
        charLett = toupper(charLett) - 'A';
        keys[charLett * 10] = key;
    }

    return charLett*10;
}

int main() {
    vector<string> arrayKeys(300);
    std::string aName("Charles");

    // No need to bother with the awkward copying.
    // std::vector and std::string will take care of it for us.

    int kPos = storeKey(arrayKeys, aName);

    if (kPos >= 0) {
        cout << "The new position in arrayKeys for 'Charles' is:  " <<
            kPos << "\ncontaining the text: " << arrayKeys[kPos] << endl;
    }

    // Don't have to remember to delete anything because nothing was new'ed.
    return 0;
}