How do I sort strings in a vector? - c++

Question

I have a program that uses something I made called "SortableVector," with a parent called SimpleVector. The Simple Vector is fine, and so is most of SortableVector, but the problem is the sort function in SortableVector. It sorts numbers just fine, but I can't get it to sort strings. Here's what I originally had:
template <class T>
void SortableVector<T>::sort()
{
T temp = 0;
for(int i = 0; i < this->size(); i++)
{
for (int count = i+1; count < this->size(); count++)
{
if(this->operator[](0) == int)
{
if (this->operator[](count) < this->operator[](i))
{
temp = this->operator[](count);
this->operator[](count) = this->operator[](i);
this->operator[](i) = temp;
count = i+1;
}
}
}
}
}
Then I tried to use the sort(begin, end) function, but that didn't work either:
template <class T>
void SortableVector<T>::sort()
{
sort(this->operator[].begin(), this->operator[].end();
}
EDIT: To help people understand the problem, here's the whole file:
#ifndef SORTABLEVECTOR_H
#define SORTABLEVECTOR_H
using namespace std;
#include "SimpleVector.h"
#include <algorithm>
#include <fstream>
#include <string>
template <class T>
class SortableVector : public SimpleVector<T>
{
public:
SortableVector(int s) : SimpleVector<T>(s)
{}
SortableVector(SortableVector &);
SortableVector(SimpleVector<T> &obj):
SimpleVector<T>(obj)
{}
void sort();
};
template <class T>
SortableVector<T>::SortableVector(SortableVector &obj):SimpleVector<T>(obj)
{
}
template <class T>
void SortableVector<T>::sort()
{
std::sort(this->operator[].begin(), this->operator[].end());
T temp = 0;
for(int i = 0; i < this->size(); i++)
{
for (int count = i+1; count < this->size(); count++)
{
if(this->operator[](0) == int)
{
if (this->operator[](count) < this->operator[](i))
{
temp = this->operator[](count);
this->operator[](count) = this->operator[](i);
this->operator[](i) = temp;
count = i+1;
}
}
}
}
}
#endif
And this is SimpleVector:
// SimpleVector.h
#ifndef SIMPLEVECTOR_H
#define SIMPLEVECTOR_H
#include <iostream>
#include <cstdlib>
using namespace std;
template <class T>
class SimpleVector
{
private:
T *aptr;
int arraySize;
void subError(); // Handles subscripts out of range
public:
SimpleVector() // Default constructor
{ aptr = 0; arraySize = 0;}
SimpleVector(int); // Constructor
SimpleVector(const SimpleVector &); // Copy constructor
~SimpleVector(); // Destructor
int size() { return arraySize; }
T &operator[](int); // Overloaded [] operator
void print() const; // outputs the array elements
void push_back(T); // newly added function (implemention needed)
T pop_back(); // newly added function (implemention needed)
};
//****************************************************************
// Constructor for SimpleVector class *
// Sets the size of the array and allocates memory for it. *
//****************************************************************
template <class T>
SimpleVector<T>::SimpleVector(int s)
{
arraySize = s;
aptr = new T [s];
}
//*********************************************
// Copy Constructor for SimpleVector class *
//*********************************************
template <class T>
SimpleVector<T>::SimpleVector(const SimpleVector &obj)
{
arraySize = obj.arraySize;
aptr = new T [arraySize];
for(int count = 0; count < arraySize; count++)
*(aptr + count) = *(obj.aptr + count);
}
// *************************************
// Destructor for SimpleVector class *
// *************************************
template <class T>
SimpleVector<T>::~SimpleVector()
{
if (arraySize > 0)
delete [] aptr;
}
//************************************************************
// SubError function *
// Displays an error message and terminates the program when *
// a subscript is out of range. *
//************************************************************
template <class T>
void SimpleVector<T>::subError()
{
cout << "ERROR: Subscript out of range.\n";
exit(0);
}
//***********************************************************
// Overloaded [] operator *
// This function returns a reference to the element *
// in the array indexed by the subscript. *
//***********************************************************
template <class T>
T &SimpleVector<T>::operator[](int sub)
{
if (sub < 0 || sub >= arraySize)
subError();
return aptr[sub];
}
//********************************************************
// prints all the entries is the array. *
//********************************************************
template <class T>
void SimpleVector<T>::print( ) const
{
for (int k = 0; k < arraySize; k++ )
cout << aptr[k] << " ";
cout << endl;
}
//***************************************************************
// (1) push_back(T val) *
// The push_back function pushes its argument onto the back *
// Of the vector. *
//***************************************************************
template <class T>
void SimpleVector<T>::push_back(T val)
{
aptr[arraySize] = val;
arraySize++;
}
// *****************************************************
// (2) pop_back() *
// The pop_back function removes the last element *
// Of the vector. It also returns that value. *
// *****************************************************
template <class T>
T SimpleVector<T>::pop_back()
{
arraySize--;
T temp = aptr[arraySize];
return temp;
}
#endif
The SimpleVector was provided by the instructor.

Answer 1

You can do without the repeated this-> 99% of the time
You can just invoke operators, instead of invoking them as functions
You can just use std::sort from <algorithm>
Imagining some of the code you didn't show:
#include <vector>
#include <algorithm>
template <typename T>
struct SimpleVector {
std::vector<T> data;
virtual ~SimpleVector() {}
};
template <typename T>
struct SortableVector : public SimpleVector<T> {
void sort() {
std::sort(this->data.begin(), this->data.end());
}
};
#include <iostream>
int main()
{
SortableVector<std::string> sv;
sv.data = {"one","two","three","four"};
sv.sort();
for(auto& s : sv.data)
std::cout << s << ' ';
}
DISCLAIMER This seems a very non-c++ way to design classes. Algorithms and containers are traditionally separated, for good reason. The exception being that member functions sometimes perform operations in more optimal ways (e.g. std::set<>::find instead of std::find)

Answer 2

It should be std::sort(aptr, aptr + arraySize);. Also you should check arraySize > 0 before doing this, if you're intending to catch errors like that instead of having undefined behaviour.
begin and end aren't magic; they rely on the object either being an array (not a pointer), or the object implementing functions .begin() and .end() that return iterators.
You could even define those functions yourself, e.g. SimpleVector<T>::begin() { return aptr; } etc. , but maybe this is not a good idea as it bypasses your bounds-checking. You'd have to actually write an iterator class instead of returning a pointer, which is more trouble than you're ready for :)
NB. Everywhere you write this->operator[](foo), it would be clearer to write (*this)[foo]