Custom Array Error || Insert() Error || DS&A Part 1 Exercise

[SuspiciousShrimp]

I am taking the first part of Mosh’s data structures and algorithms course, and I am trying to create an adjustable array from scratch that can print, insert, find an index of, and remove at the index of. I am running into an error that I can’t find.

The Error:

Undefined symbol: Array<std::__1::basic_string<char, std::__1::char_traits, std::__1::allocator>>::Array(int)

Array.cpp:

#include "Array.hpp"
#include <iostream>

template<typename T>
Array<T>::Array(int length) : length(length) {
    newArray = new T[length];
}

template<typename T>
void Array<T>::insert(T value) {
    if ( size(newArray) == length){
        T newerArray = new T[length++];
        for(int i = 0; i < size(newArray); i++){
            newerArray[i] = newArray[i];
        }
        delete[] newArray;
        newerArray[elem++] = value;
    } else {
        newArray[elem] = value;
        elem++;
    }
}

template<typename T>
void Array<T>::print(){
    for(T val : newArray)
        std::cout << val;
}

template<typename T>
void Array<T>::removeAt(int index){
    for (int i = index - 1; i < size(newArray) - 1; ++i)
        newArray[i] = newArray[i + 1];
}

template<typename T>
int Array<T>::indexOf(T value){
    for (int i = 0; i < size(newArray); i++){
        if (newArray[i] == value)
            return i;
    }
    return -1;
}

template<typename T>
Array<T>::~Array() {
    delete[] newArray;
}

Array.hpp:

template <typename T>
class Array {
public:
    Array(int length);
    ~Array();
    void insert(T value);
    void print();
    void removeAt(int index);
    int indexOf(T value);
private:
    T *newArray;
    int elem = 0;
    int length;
};

Main File:

#include <iostream>
#include "Array.hpp"
#include <string>

int main() {
    Array<std::string> array(3);
    
    return 0;
}

I have a question and a request to ask.

1. How can I fix the error in this code?
2. How can I decode the error I sent so that I can solve this on my own next time?

C++

[POMPOMBALLS]

@SuspiciousShrimp

How can I fix the error in this code?

@SuspiciousShrimp

The Error:

Undefined symbol: Array<std::__1::basic_string<char, std::__1::char_traits, std::__1::allocator>>::Array(int)

Worked fine on an online compiler. Try changing the name of your constructor parameter. Though on checking your functions you would find following issues (read comments):

@SuspiciousShrimp

Array.hpp:

template <typename T>
class Array {
public:
    Array(int length);    // default constructor can still be created
                          // use Array() = delete; or use some other
                          // workaround to prevent errors
    ~Array();
    void insert(T value);
    void print();
    void removeAt(int index);
    int indexOf(T value);
private:
    T *newArray;    // always initialize pointers with
                    // nullptr or a known value
    int elem = 0;    // try a more generic name like total_elements
                     // though not much of an issue
    int length;
};

@SuspiciousShrimp

Array.cpp:

#include "Array.hpp"
#include <iostream>

template<typename T>
Array<T>::Array(int length) : length(length) {    // keep separate names to prevent confusion
                                                  // generally an underscore is applied to the parameter
                                                  // Array(int _length)
    newArray = new T[length];
}

template<typename T>
void Array<T>::insert(T value) {
    if ( size(newArray) == length){    // std::size() is an overloaded member function
                             // not generic template function
                             // also, size is already equal to length
                             // use total_elements (here elem)
                             // and compare with length - 1
        T newerArray = new T[length++];    // newerArray is a pointer
                                           // but it is not declared as one
        for(int i = 0; i < size(newArray); i++){
            newerArray[i] = newArray[i];
        }
        delete[] newArray;    // you are not reassigning newArray
                              // newArray is now a dangling pointer
        newerArray[elem++] = value;
    } else {
        newArray[elem] = value;
        elem++;
    }
}

template<typename T>
void Array<T>::print(){
    for(T val : newArray)    // range based for loops cannot be used
                             // for dynamic arrays without begin / end pointers
        std::cout << val;
}

template<typename T>
void Array<T>::removeAt(int index){
    for (int i = index - 1; i < size(newArray) - 1; ++i)
        newArray[i] = newArray[i + 1];
}    // length of array is still the same
     // value of total_elements (elem) is still the same
     // perform copy to another array
     // to prevent memory leaks

template<typename T>
int Array<T>::indexOf(T value){
    for (int i = 0; i < size(newArray); i++){
        if (newArray[i] == value)
            return i;
    }
    return -1;
}

template<typename T>
Array<T>::~Array() {
    delete[] newArray;    // also set newArray to nullptr
                          // to prevent dangling pointer
}

@SuspiciousShrimp

How can I decode the error I sent so that I can solve this on my own next time?

1. Learn the language
2. Learn its programming practices
3. Keep the code readable
4. A few blank lines to group similar content do not have any issue on performance
5. Create a program to solve a problem
6. On successful creation, try to make it more readable
7. Parse your code manually and remove or modify commands for optimization
8. Keep the code readable
9. Practice to get comfortable in creating programs
10. Practice and understand what is happening in the code

Try to solve the mentioned problems on your own. I used an online compiler (as my drive is corrupt) so it took a while. Though I have modified your code to make it work, I will not paste the code here before you try to solve it. Try reading the documentation or Stack Overflow or other forums to get your programming query resolved.