control may reach end of non-void function

[gambette]

Good day to all! I'm experiencing some issue with my custom 'vector' template class that I'm required to built to understand how the mechanism of a STL vector work. However one of the template function kept returning a 'control may reach end of non-void function. A quick search on the error and mainly its because the compiler is expecting a 'return'. But I've already achieved that. I'm using Xcode v9.4.1

e.g.

  template <class elemType>
elemType& Vector<elemType>::at(int i)
{
    if ((i >= 0) && (i<length)) {
        return list[i];
    }
}

the full class is here:

#ifndef Vector_hpp
#define Vector_hpp

#include <iostream>
#include <string>
#include <iomanip>
#include <fstream>
#include <sstream>


using namespace std;

template <class elemType>
class Vector
{
public:
    
    Vector(); //constructor
    ~Vector();//destructor
    
    //Functions
    void create(int n);
    void push_back(const elemType& i);
    void pop_back();
    void print() const;
    void resize(int newsize);
    
    int size() const;
    int capSize() const;
    elemType& at(int i);
    
    //Array Functions
    bool isEmpty() const;
    bool isFull() const;
    
private:
    elemType *list;
    int length;
    int maxSize;
    
};

template <class elemType>
Vector<elemType>::Vector() // constructor
{
    create(2);
}

template <class elemType>
Vector<elemType>::~Vector() //destructor
{
    delete[]list;
}

template <class elemType>
void Vector<elemType>::create(int n)
{
    list = new elemType[n]; //create array of size n
    
    maxSize = n;
    length = 0;
}

template <class elemType>
void Vector<elemType>::push_back(const elemType& i)
{
    
    if (length >= maxSize)
    {
        resize(maxSize * 2); //increase the array size
    }
    list[length] = i;
    length++; //increase the length to keep track
}

template <class elemType>
void Vector<elemType>::pop_back()
{
    length--;
}

template <class elemType>
void Vector<elemType>::print() const
{
    for (int i = 0; i < length; i++)
    {
        cout << list[i] << " ";
        cout << endl;
    }
}

template <class elemType>
int Vector<elemType>::size() const
{
    return length;
}

template <class elemType>
void Vector<elemType>::resize(int newSize)
{
    elemType *newList = new elemType[newSize];
    elemType *newListPointer = newList;
    elemType *oldListPointer = list;
    
    //copy data from old array to new array
    while (oldListPointer != (list + length)) //while not yet at a blank position
    {
        *(newListPointer) = *(oldListPointer); //copy the value to the new position
        newListPointer++; //shift the pointer
        oldListPointer++;
    }
    
    maxSize = newSize;
    
    //throw away old Array
    delete[] list;
    list = newList;
}

template <class elemType>
int Vector<elemType>::capSize() const
{
    return maxSize;
}

template <class elemType>
elemType& Vector<elemType>::at(int i)
{
    if ((i >= 0) && (i<length)) {
        return list[i];
    }
}

template <class elemType>
bool Vector<elemType>::isEmpty() const
{
    return (length == 0);
}

template <class elemType>
bool Vector<elemType>::isFull() const
{
    return (length == maxSize);
}


#endif /* Vector_hpp */

[Repeater]

If that if statement is not true, then where is the return?

How does that function return when the statement ((i >= 0) && (i<length)) is false?

[gambette]

@repeater do you mean that I should include a 'else' part and return something in it?

[Repeater]

You could do that. Or you could just have a return at the end on its own:

template <class elemType>
elemType& Vector<elemType>::at(int i)
{
    if ((i >= 0) && (i<length)) {
        return list[i];
    }
    else
   {
      // Uh oh - what do you do here?
     return ...   // return what?
   }
}

or

template <class elemType>
elemType& Vector<elemType>::at(int i)
{
    if ((i >= 0) && (i<length)) {
        return list[i];
    }

      // Uh oh - what do you do here?
     return ...   // return what?
}

Either of these will fix the problem. But what should you return? If someone using your vector class asks for contents of element 50 , but the vector doesn't have an element 50 because the vector is smaller than that, what should you return? This is something you need to think about.