C++: Program crash while adding object to custom vector class - c++

Question

I'm working on an email validation program for my cmpsci class and am having trouble with this one part.
What I'm doing is reading a list of valid top level domains from a text file into a vector class I wrote myself (I have to use a custom vector class unfortunately). The problem is that the program reads in and adds the first few domains to the vector all well and fine, but then crashes when it gets to the "org" line. I'm completely stumped why it works for the first few and then crashes.
Also, I have to use a custom string class; that's why I have the weird getline function (so I get the input in a char* for my String constructor). I've tried using the standard string class with this function and it still crashed in the same way so I can rule out the source of the problem being my string class. The whole program is quite large so I am only posting the most relevant parts. Let me know if more code is needed please. Any help would be awesome since I have no clue where to go from here. Thanks!
The ReadTlds function:
void Tld::ReadTlds() {
// Load the TLD's into the vector
validTlds = Vector<String>(0); // Init vector; declaration from header file: "static Vector<String>validTlds;"
ifstream in(TLD_FILE);
while(!in.eof()) {
char tmpInput[MAX_TLD_LENGTH]; // MAX_TLD_LENGTH equals 30
in.getline(tmpInput, MAX_TLD_LENGTH);
validTlds.Add(String(tmpInput)); // Crashes here!
}
}
My custom vector class:
#pragma once
#include <sstream>
#define INIT_CAPACITY 100
#define CAPACITY_BOOST 100
template<typename T> class Vector {
public:
// Default constructor
Vector() {
Data=NULL;
size=0;
capacity=INIT_CAPACITY;
}
// Init constructor
Vector(int Capacity) : size(0), capacity(Capacity) {
Data = new T[capacity];
}
// Destructor
~Vector() {
size=0;
Data = NULL;
delete[] Data;
}
// Accessors
int GetSize() const {return size;}
T* GetData() {return Data;}
void SetSize(const int size) {this->size = size;}
// Functions
void Add(const T& newElement) {
Insert(newElement, size);
}
void Insert(const T& newElement, int index) {
// Check if index is in bounds
if((index<0) || (index>capacity)) {
std::stringstream err;
err << "Vector::Insert(): Index " << index << " out of bounds (0-" << capacity-1 << ")";
throw err.str();
}
// Check capacity
if(size>=capacity)
Grow();
// Move all elements right of index to the right
for(int i=size-1; i>=index; i--)
Data[i+1]=Data[i];
// Put the new element at the specified index
Data[index] = newElement;
size++;
}
void Remove(int index) {
// Check if index is in bounds
if((index<0) || (index>capacity-1)) {
std::stringstream err;
err << "Vector::Remove():Index " << index << " out of bounds (0-" << capacity-1 << ")";
throw err.str();
}
// Move all elements right of index to the left
for(int i=index+1; i<size; i++)
Data[i-1]=Data[i];
}
// Index operator
T& operator [] (int index) const {
// Check if index is in bounds
if((index<0) || (index>capacity-1)) {
std::stringstream err;
err << "Vector operator[]:Index " << index << " out of bounds (0-" << capacity-1 << ")";
throw err.str();
}
return Data[index];
}
// Assignment oper
Vector<T>& operator = (const Vector<T>& right) {
Data = new T[right.GetSize()];
for(int i=0; i<right.GetSize(); i++)
Data[i] = right[i];
size = right.GetSize();
return *this;
}
private:
T *Data;
int size; // Current vector size
int capacity; // Max size of vector
void Grow() {
capacity+=CAPACITY_BOOST;
T* newData = new T[capacity];
for(int i=0; i<capacity; i++)
newData[i] = Data[i];
// Dispose old array
Data = NULL;
delete[] Data;
// Assign new array to the old array's variable
Data = newData;
}
};
The input file:
aero
asia
biz
cat
com
coop
edu
gov
info
int
jobs
mil
mobi
museum
name
net
org <-- crashes when this line is read
pro
tel
travel
The error Visual Studio throws is:
Unhandled exception at 0x5fb04013 (msvcp100d.dll) in Email4.exe: 0xC0000005: Access violation reading location 0xabababbb.

Answer 1

The problem is in your grow function:
void Grow() {
capacity+=CAPACITY_BOOST;
T* newData = new T[capacity];
for(int i=0; i<capacity; i++)
newData[i] = Data[i];
You increase the capacity, but then copy elements that didn't exist in the old array. It should be something like:
void Grow() {
int old_capacity = capacity;
capacity+=CAPACITY_BOOST;
T* newData = new T[capacity];
for(int i=0; i<old_capacity; i++)
newData[i] = Data[i];
You also NULL out Data before deleting it in both Grow and the destructor, which causes a memory leak. In both cases, you really don't need to set it to NULL at all, since there's no change of it being accidentally double-deleted (in Grow it's set to a new pointer immediately, in the destructor the object's lifetime is over). So just
delete[] Data;
alone is fine.
Also I think
if(size>=capacity)
can be:
if(size == capacity)
since size should never be over capacity. That would mean you'd already overflowed the buffer.

Answer 2

Matthew is probably right. Still, there's a valuable lesson to be learned here.
When you hit a problem like this, don't stop walking your code in your ReadTlds function. Keep walking inside the Vector class. Functions like Insert and Grow probably hold the error, but if you don't walk through them, you'll never find it.
Debugging is it's own very special skill. It takes a long time to get it down pat.

Answer 3

edit it's a late night and I misread your code, but I left my post to comment back

Answer 4

Also in the default ctor you do
Data = NULL;
capacity=INIT_CAPACITY;
(EDIT: expanded explanation here)
But never allocate the memory for Data. Shouldn't it be:
Vector() {
Data= new T[INIT_CAPCITY];
size=0;
capacity=INIT_CAPACITY;
}
And remove is missing
--size
EDIT:
Fellow readers help me out here:
Data is of type T* but everywhere else you are assigning and allocating it just like T instead of T* . My C++ days are too long gone to remember whether using a T& actually resolves this.
Also I can't remember that if you have an array of pointers and destruct it, that the dtor for the single instances in the array are destroyed.
Also in the assignment operator, wouldn't you be copying the pinters? so you just have to rely on the fact the the instance where you copyid from is never deleted (because then your objects would be dead too).
hth Mario