动态字符串数组构造函数和null返回

Question

class DSArray {

private:
    int size;
    string *dynamicArray;

public:
    DSArray();
    DSArray(int size, string []);
    ~DSArray();
    int getSize() const;
    void addEntry(string newString);
    bool deleteEntry(string find);
    string getEntry(const int index) const;
    void operator = (const DSArray& obj);
    string operator [] (int index);
    friend ostream& operator << (ostream &out, const DSArray& array);


};

DSArray::DSArray(){
    size = 0;
    dynamicArray = NULL;
}

DSArray::DSArray(int size, string []){
    dynamicArray = new string[size];
    for (int i = 0; i < size; i++){
        dynamicArray[i] = getEntry(i);
    }
    size = getSize();
}

DSArray::~DSArray(){
    delete[] dynamicArray;
}

int DSArray::getSize() const{
    return size;
}


void DSArray::addEntry(string newString){
    string *tempPtr = dynamicArray;
    dynamicArray = new string[size + 1];
    dynamicArray[size].assign(newString);
    for(int i = 0; i < size; i++){
        dynamicArray[i] = tempPtr[i];
    }
    if(size > 0){
        delete[] tempPtr;
    }
    size++;
}

ostream& operator << (ostream &out, const DSArray& array){
    for (int i = 0; i < array.getSize(); i++)
        out << array.dynamicArray[i];
    return out;
}



bool DSArray::deleteEntry(string toDelete)
{
    int index;
    for(index = 0; index < size; index++)
    {
        if(dynamicArray[index] == toDelete) break;
    }

    if(index == size) return false;

    string *newArray = new string[size--];

    int i;
    for(i = 0; i < index; i++) newArray[i] = dynamicArray[i];
    for(int k = index + 1; k <= size; k++, i++) newArray[i] = dynamicArray[k];

    delete [] dynamicArray;
    dynamicArray = newArray;

    return true;
}

string DSArray::getEntry(const int index) const{
    static string emptyStr = "";
    if(index > size){
        return emptyStr;
    }
    else{
        return dynamicArray[index];
    }

}


void DSArray::operator = (const DSArray& obj){
    DSArray temp(obj);
    if(this->size != 0)
        delete[] this->dynamicArray;
    this->size = obj.getSize();
    this->dynamicArray = new string [this->size];
    for(int i = 0; i < this->size; i++)
        this->dynamicArray[i] = obj.getEntry(i);
}

string DSArray::operator [] (int index){
    string emptyString = "";
    if (index >= size){
        return emptyString;
    }
    return dynamicArray[index];
}

int main()

{
    DSArray foods;
    string x[] = {"Burrito", "Sushi", "Pizza"};
    DSArray A(3, x);
    cout << A;
    A[3] = "Spaghetti";
    foods.addEntry("Steak");
    foods.deleteEntry("Sushi");




    return 0;

}

I'm trying to test my functions in main but it's not actually displaying anything in the console. I was told that my constructor isn't setting the size correctly because calling getSize returns the object's size which hasn't been initialized yet. How exactly do i fix this? Also does anyone know if the getEntry function get return a null instead of an empty string? My assignment says it should return a null, however, when i do return a null it gives me a runtime error. Any help is appreciated. Thanks!

Answer 1

You are not initializing the member variable size in the constructor. Use:

DSArray::DSArray(int size, string input[]) : size(size) { ... }

Also, the line

    dynamicArray[i] = getEntry(i);

does not do anything useful. It is essentially self assignment.

You can avoid hard to follow code by using a different name for input argument. Also, copy the array of input strings to the member variable.

DSArray::DSArray(int sizeIn, string input[]) : size(sizeIn) {
    dynamicArray = new string[size];
    for (int i = 0; i < size; i++){
        dynamicArray[i] = input[i];
    }
}