GCC "AddressSanitizer: heap-buffer-overflow" when initializing struct - c++

I've been writing an VM/Interpreter combination thingy, I don't know how to exactly describe it.
Everything behaved as it should, now before I have hundreds of lines of code, I wanted to go into Garba Collection, because there were some pointers which somehow got lost, in some way. Not that I didn't delete pointers, I created, but they somehow got lost in the proccess of interpreting/running the code.
So, I wanted to track them. I wrote my own "Memory Manager" in some way, it's just a std::vector, where I collect all pointers in.
To track and allocate pointers, I have following code:
struct MemBlock {
bool free;
void* ptr;
size_t size;
};
std::vector<MemBlock*> mem;
size_t max_size;
size_t mem_size;
int count = 0;
void mem_init(size_t maxSize) {
max_size = size/sizeof(MemBlock*);
}
void* mem_alloc(size_t size) {
for (int i = 0; i < count; i++) {
MemBlock* block = mem[i];
if (block->free) {
mem_size -= block->size;
mem_size += size;
block->free = false;
block->ptr = malloc(size);
block->size = size;
if (block->ptr == nullptr) {
throw std::exception();
}
return block->ptr;
}
}
void* ptr = malloc(sizeof(size));
if (ptr == nullptr) {
throw PointerNullException();
}
MemBlock* block = (MemBlock*) malloc(sizeof(MemBlock));
*block = (MemBlock) {
false,
ptr,
size
};
mem_size += size;
count++;
mem.push_back(block);
return block->ptr;
}
But as soon, as I use mem_alloc() and initialize the object inside of the pointer:
Int* i = (Int*) mem_alloc(sizeof(Int));
*i = (Int) {}; // -- Here
i->value = atoi(advance().c_str());
The GCC AdressSanitizer shows following error:
==5939==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000098 at pc 0x555963d82fc5 bp 0x7fff4ec39070 sp 0x7fff4ec39060
WRITE of size 4 at 0x602000000098 thread T0
If I remove said line, then it just occurs on the nex line. The the pointer does point to a valid memory location, if not it should've had thrown an exception.
I'm sure that I missed something/did something wrong, of course.
But I don't know what. This is how I learned it, or at least what I understood...
Edit:
This would be a minimal reproducible Example:
#include <iostream>
#include <stdlib.h>
#include <vector>
struct Object {
const char* type;
};
template <typename T>
struct Primitive : Object {
T value;
};
struct Int : Primitive<int> {
const char* type = "int";
};
struct MemBlock {
bool free;
void* ptr;
size_t size;
};
std::vector<MemBlock*> mem;
size_t mem_size = 0;
int count = 0;
void* mem_alloc(size_t size) {
for (int i = 0; i < count; i++) {
MemBlock* block = mem[i];
if (block->free) {
mem_size -= block->size;
mem_size += size;
block->free = false;
block->ptr = malloc(size);
block->size = size;
if (block->ptr == nullptr) {
throw std::exception();
}
return block->ptr;
}
}
void* ptr = malloc(sizeof(size));
MemBlock* block = (MemBlock*) malloc(sizeof(MemBlock));
*block = (MemBlock) {
false,
ptr,
size
};
mem_size += size;
count++;
mem.push_back(block);
std::cout << "HI" << std::endl;
return block->ptr;
}
void mem_free(void* ptr) {
for (int i = 0; i < count; i++) {
MemBlock* block = mem[i];
if (block->ptr == ptr) {
free(ptr);
mem_size -= block->size;
block->size = 0;
block->ptr = nullptr;
block->free = true;
}
}
}
int main() {
// Create new Integer-Object
Int* i = (Int*) mem_alloc(sizeof(Int));
std::cout << "[Pointer]: " << i << std::endl;
*i = (Int) {};
i->value = 5;
std::cout << "[Value]: " << i->value << std::endl;
}

Well, thanks to Retired Ninja and Richar Critten, I've got the solution.
In mem_alloc() I've used sizeof(size) to allocate memory to the pointer, which of course is wrong. I guess my head was pretty much off after hours of coding.
But I guess this problem is now solved.

Related

C++ segmentation fault using dynamic arrays of strings

My string-dynamic-array.cpp file
#include <iostream>
#include <string>
class DynamicArray
{
public:
DynamicArray()
: mCapacity(1), mNumberOfElements(0)
{
mArray = new std::string[mCapacity];
}
DynamicArray(int size)
: mCapacity(size), mNumberOfElements(0)
{
mArray = new std::string[mCapacity];
}
DynamicArray(const DynamicArray& array)
: mCapacity(array.getCapacity()), mNumberOfElements(array.length())
{
mArray = new std::string[mCapacity];
for (size_t i = 0; i < mCapacity; ++i)
{
mArray[i] = array.get(i);
}
}
~DynamicArray()
{
delete[] mArray;
}
void add(std::string element)
{
if (mNumberOfElements >= mCapacity)
{
expand();
}
mArray[mNumberOfElements++] = element;
}
std::string get(int index) const
{
if (index > mNumberOfElements)
{
std::string exception = std::to_string(index) + " index is out of bounds.";
std::cout << exception;
return std::string();
}
if (index < 0)
{
if (mNumberOfElements + index < 0)
{
std::string exception = std::to_string(index) + " index result in " + std::to_string(mNumberOfElements + index) + " which is out of bounds.\n";
std::cout << exception;
return std::string();
}
return mArray[mNumberOfElements + index];
}
return mArray[index];
}
int length() const
{
return mNumberOfElements;
}
int getCapacity() const
{
return mCapacity;
}
private:
int mCapacity;
int mNumberOfElements;
std::string* mArray;
void initialize(int from)
{
for (size_t i = from; i < mCapacity; ++i)
{
mArray[i] = std::string();
}
}
void expand()
{
mCapacity *= 2;
std::string* temporaryArray = new std::string[mCapacity];
for (size_t i = 0; i < mCapacity; ++i)
{
temporaryArray[i] = mArray[i];
}
delete[] mArray;
mArray = temporaryArray;
initialize(mNumberOfElements);
}
};
int main()
{
DynamicArray strings;
strings.add("Hello");
strings.add("World");
for (size_t i = 0; i < strings.length(); ++i)
{
std::cout << strings.get(i) << std::endl;
}
}
My output
$ clang++ tests/string-dynamic-array.cpp -o tests/string-dynamic-array && ./tests/string-dynamic-array
[1] 14950 segmentation fault (core dumped) ./tests/string-dynamic-array
I get a segmentation fault.
The issue as far as I've found is in the code where I expand the array, in the expand() function. I think it's in the for loop because the index of for loop is out of bounds of the original array.
I've tried this with int, it seems to work fine. How can I do this with strings?
As commented by UnholySheep.
I changed my expand function a bit so the loop only runs till the size of the old array.
Updated expand function:
void expand()
{
mCapacity *= 2;
std::string* temporaryArray = new std::string[mCapacity];
for (size_t i = 0; i < mNumberOfElements; ++i)
{
temporaryArray[i] = mArray[i];
}
delete[] mArray;
mArray = temporaryArray;
initialize(mNumberOfElements);
}
In “expand” method you have deleted mArray, then, you copied the temporaryArray to it, while as far as I know, mArray’s handle is not valid anymore. You need to pass temporaryArray‘s handle to mArray so you could use it as a new expanded array.

Difference in allocating char type and int type in C++

I have a class foo like this:
class foo
{
private:
int* a;
public:
foo()
{
a = new int[4];
cout << "a" << endl;
}
};
When I create new object named foo1 and then I debug, after the allocating line, it yields the result: a 0x005a4580 {-842150451}.
But when I replace all int-s by char-s in class definition, it yields an undesired result:
a 0x005694a0 "ÍÍÍÍýýýý\x6ŒÒ•\x5Ÿ"
that the size of a is now greater than 4.
I dont know what happened. Could you please give me an explanation?
Full code:
#include <iostream>
#include <string>
using namespace std;
class String
{
public:
String(char* data)
{
setSize(0);
while (*(data + size) != '\0')
size++;
this->data = new char[size];
//need to allocate memory for 'data' pointer because 'data' pointer is now on the stack and the data must be on the heap
memcpy(this->data, data, size * sizeof(char));
}
void operator=(String rhs)
{
if (this->data != NULL)
delete[] this->data, data = NULL;
this->data = new char[rhs.getSize()]; //allocate
memcpy(this->data, data, size * sizeof(char));
}
int getSize()
{
setSize(0);
while (*(data + size))
size++;
return size;
}
void setSize(int size)
{
this->size = size;
}
void display()
{
for (int i = 0; i < size; i++)
cout << *(data + i);
}
~String()
{
if (data != NULL)
delete[] data, data = NULL;
}
private:
char* data;
int size;
};
void main()
{
String a("abcd");
String b("1");
a.display();
cout << endl;
cout << b.getSize() << endl;
a = b;
cout << a.getSize() << endl;
system("pause");
}
Whatever you're using to look at a doesn't know how much you allocated. It just knows the type.
In the first version it sees int *, so it shows a single int.
In the second version it sees char *, so it assumes it's a C string and prints whatever is in memory up to the first '\0' byte.

Exception Error : Access violation reading location 0xDDDDDDDD

I am trying to create a dynamic string array in c++. When trying to display the contents of my dynamic string array to the console I receive this error:
Exception thrown at 0x0FD670B6 (msvcp140d.dll) in Assignment4.exe: 0xC0000005: Access violation reading location 0xDDDDDDDD.
Here is my code:
DynamicStringArray.h
#pragma once
#include "stdafx.h"
#include <string>
#include <iostream>
using namespace std;
class DynamicStringArray
{
public:
DynamicStringArray();
DynamicStringArray(DynamicStringArray &array);
~DynamicStringArray();
int getSize();
void displayContents();
void addEntry(const string &addElement);
string getEntry(int index);
int deleteEntry(const string &deleteElement);
private:
string *dynamicArray;
int size;
};
DynamicStringArray.cpp
#include "stdafx.h"
#include "DynamicStringArray.h"
#include <string>
#include <iostream>
using namespace std;
DynamicStringArray::DynamicStringArray()
{
dynamicArray = NULL;
size = 0;
}
DynamicStringArray::DynamicStringArray(DynamicStringArray &array)
{
if (dynamicArray != NULL)
{
size = 0;
delete [] dynamicArray;
dynamicArray = NULL;
}
size = array.getSize();
dynamicArray = new string[size];
for (int i = 0; i < size; i++)
dynamicArray[i] = array.dynamicArray[i];
}
DynamicStringArray::~DynamicStringArray()
{
cout << "In destructor." << endl;
delete [] dynamicArray;
dynamicArray = NULL;
}
int DynamicStringArray::getSize()
{
return size;
}
void DynamicStringArray::displayContents()
{
if (size != 0)
for (int i = 0; i < size; i++)
cout << "Item-" << i << ": " << dynamicArray[i] << endl;
else
cout << "Array is empty." << endl;
}
void DynamicStringArray::addEntry(const string &addElement)
{
string *temp = new string[size + 1];
for (int i = 0; i < size; i++)
temp[i] = dynamicArray[i];
temp[size] = addElement;
size++;
delete [] dynamicArray;
dynamicArray = temp;
delete[] temp;
}
string DynamicStringArray::getEntry(int index)
{
if ((index >= 0) && (index < size))
{
return dynamicArray[index];
}
return NULL;
}
int DynamicStringArray::deleteEntry(const string &deleteElement)
{
if(size == 0)
{
return false;
}
for (int i = 0; i < size; i++)
{
if (dynamicArray[i] == deleteElement)
{
string *temp = new string[size - 1];
for (int x = 0; x < size - 1; ++x)
{
if (x < i)
temp[x] = dynamicArray[x];
else
temp[x] = dynamicArray[x + 1];
}
delete[] dynamicArray;
dynamicArray = temp;
delete[] temp;
--size;
return true;
}
}
return false;
}
main:
int main()
{
DynamicStringArray dsArray1;
cout << "dsArray1.displayContents():" << endl;
dsArray1.displayContents(); // Should indicate array is empty
cout << "Display dsArray1.getSize()= " << dsArray1.getSize() << endl;
dsArray1.addEntry("Entry-A");
dsArray1.displayContents();
dsArray1.addEntry("Entry-B");
dsArray1.displayContents();
dsArray1.addEntry("Entry-C");
dsArray1.displayContents();
return 0;
}
Can anyone tell me what I am doing wrong. How can i fix this problem?
Please note that all of this is already available by utilizing
std::vector<std::string>. The std::vector class is the dynamic array class that C++ provides, and there is little to no reason to make home-made versions of what is available to you.
Having said this, one glaring issue is that your copy constructor is incorrect. The dynamicArray is uninitialized, but you use it here:
if (dynamicArray != NULL)
There is no guarantee what value dynamicArray has. The fix is to remove this entire block of code in the copy constructor:
if (dynamicArray != NULL)
{
size = 0;
delete [] dynamicArray;
dynamicArray = NULL;
}
Since the copy constructor constructs a brand new object, there is no reason to "pretest" for a NULL pointer and thus do unnecessary work. Remember that the object did not exist, so there is nothing preliminary to do.
The second issue is that you're issuing a delete [] temp; call in the addEntry and deleteEntry functions. Remove these lines, as you are deallocating the memory that you've just assigned to dynamicArray.
The third issue is that you're missing the user-defined assignment operator. The assignment operator has the following signature, and you need to provide the implementation:
DynamicStringArray& operator=(const DynamicStringArray& );
Without this function, assigning a DynamicStringArray to another DynamicStringArray will cause memory leaks and double deallocation of memory when both objects go out of scope.
One implementation can use the copy / swap idiom:
#include <algorithm>
//...
DynamicStringArray& DynamicStringArray::operator=(const DynamicStringArray& rhs)
{
DynamicStringArray temp(rhs);
std::swap(temp.dynamicArray, dynamicArray);
std::swap(temp.size, size);
return *this;
}
Another issue is this:
string DynamicStringArray::getEntry(int index)
{
if ((index >= 0) && (index < size))
{
return dynamicArray[index];
}
return NULL; // <-- Undefined behavior if this is done
}
It is undefined behavior to assign a std::string object with NULL. Either return an empty string, or throw an exception if the index is out of bounds.
In conclusion, I highly recommend that you read up on the Rule of 3 when it comes to designing classes that must implement correct copy semantics.

Minimal C++ STL Vector Implementation Problems

I have a technical problem and it's really confusing me. I apologise in advance because I may not be giving the relevant details; I don't yet why it's going wrong and it would be excessive to include all the code I'm working with.
I'm working with a large program that uses the C++ STL. I'm moving this code to a very sensitive environment without a standard clib nor STL implementaton; it will redefine malloc/free/new/delete etc... For that, I need to replace the std:: parts with my own simplified implementations. I've started with std::vector. Right now it's running in the standard ecosystem so it's the GNU libc and STL. The only thing that's changed is this vector class.
When I execute the program with the replaced class, it segfaults. I've put this through GDB and found that the program will request an object from the vector using the subscript operator. When the object reference is returned, a method is invoked and the program segfaults. It seems it can't find this method and ends up in main_arena() in GDB. The type of the object is an inherited class.
I'm really not sure at all what the problem is here. I would love to provide additional details, but I'm not sure what more I can give. I can only assume something is wrong with my vector implementation because nothing else in the program has been changed. Maybe there's something obvious that I'm doing wrong here that I'm not seeing at all.
I'm using: g++ (GCC) 4.4.5 20110214 (Red Hat 4.4.5-6)
I'd really appreciate any feedback/advice!
#ifndef _MYSTL_VECTOR_H_
#define _MYSTL_VECTOR_H_
#include <stdlib.h>
#include <assert.h>
typedef unsigned int uint;
namespace mystl
{
/******************
VECTOR
********************/
template <typename T>
class vector
{
private:
uint _size;
uint _reserved;
T *storage;
void init_vector(uint reserve)
{
if (reserve == 0)
{
_reserved = 0;
return;
}
storage = (T*)malloc(sizeof(T)*reserve);
assert(storage);
_reserved = reserve;
}
public:
vector()
{
// std::cerr << "default constructor " << this << std::endl;
storage = NULL;
_size = 0;
_reserved = 0;
}
vector(const vector<T> &other)
{
// std::cerr << "copy constructor " << this << std::endl;
storage = NULL;
_size = 0;
_reserved = 0;
init_vector(other.size());
_size = other.size();
for (uint i=0; i<other.size(); i++)
{
storage[i] = T(other[i]);
}
}
vector(uint init_num, const T& init_value)
{
// std::cerr << "special constructor1 " << this << std::endl;
storage = NULL;
_size = 0;
_reserved = 0;
init_vector(init_num);
for (size_t i=0; i<init_num; i++)
{
push_back(init_value);
}
}
vector(uint init_num)
{
// std::cerr << "special constructor2 " << this << std::endl;
storage = NULL;
_size = 0;
_reserved = 0;
init_vector(init_num);
}
void reserve(uint new_size)
{
if (new_size > _reserved)
{
storage = (T*)realloc(storage, sizeof(T)*new_size);
assert(storage);
_reserved = new_size;
}
}
void push_back(const T &item)
{
if (_size >= _reserved)
{
if (_reserved == 0) _reserved=1;
reserve(_reserved*2);
}
storage[_size] = T(item);
_size++;
}
uint size() const
{
return _size;
}
~vector()
{
if (_reserved)
{
free(storage);
storage = NULL;
_reserved = 0;
_size = 0;
}
}
// this is for read only
const T& operator[] (unsigned i) const
{
// do bounds check...
if (i >= _size || i < 0)
{
assert(false);
}
return storage[i];
}
T& operator[] (unsigned i)
{
// do bounds check...
if (i >= _size || i < 0)
{
assert(false);
}
return storage[i];
}
// overload = operator
const vector<T>& operator= (const vector<T>& x)
{
// check for self
if (this != &x)
{
_reserved = 0;
_size = 0;
storage = NULL;
init_vector( x.size() );
for(uint i=0; i<x.size(); i++)
{
storage[i] = T(x[i]);
}
_size = x.size();
}
return *this;
}
uint begin() const
{
return 0;
}
void insert(uint pos, const T& value)
{
push_back(value);
if (size() == 1)
{
return;
}
for (size_t i=size()-2; i>=pos&& i>=0 ; i--)
{
storage[i+1] = storage[i];
}
storage[pos] = value;
}
void erase(uint erase_index)
{
if (erase_index >= _size)
{
return;
}
//scoot everyone down by one
for (uint i=erase_index; i<_size; i++)
{
storage[i] = storage[i+1];
}
_size--;
}
void erase(uint start, uint end)
{
if (start > end)
{
assert(false);
}
if (end > _size)
end = _size;
for (uint i=start; i<end; i++)
{
erase(start);
}
assert(false);
}
void clear()
{
erase(0,_size);
}
bool empty() const
{
return _size == 0;
}
}; //class vector
}
#endif // _MYSTL_VECTOR_H_
Wow!
Your assignment operator also leaks memory.
Becuause you are using malloc/release the constructor to your type T will will not be called and thus you can not use your vector for anything except the most trivial of objects.
Edit:
I am bit bored this morning: Try this
#include <stdlib.h> // For NULL
#include <new> // Because you need placement new
// Because you are avoiding std::
// An implementation of swap
template<typename T>
void swap(T& lhs,T& rhs)
{
T tmp = lhs;
lhs = rhs;
rhs = tmp;
}
template <typename T>
class vector
{
private:
unsigned int dataSize;
unsigned int reserved;
T* data;
public:
~vector()
{
for(unsigned int loop = 0; loop < dataSize; ++loop)
{
// Because we use placement new we must explicitly destroy all members.
data[loop].~T();
}
free(data);
}
vector()
: dataSize(0)
, reserved(10)
, data(NULL)
{
reserve(reserved);
}
vector(const vector<T> &other)
: dataSize(0)
, reserved(other.dataSize)
, data(NULL)
{
reserve(reserved);
dataSize = reserved;
for(unsigned int loop;loop < dataSize;++loop)
{
// Because we are using malloc/free
// We need to use placement new to add items to the data
// This way they are constructed in place
new (&data[loop]) T(other.data[loop]);
}
}
vector(unsigned int init_num)
: dataSize(0)
, reserved(init_num)
, data(NULL)
{
reserve(reserved);
dataSize = reserved;
for(unsigned int loop;loop < dataSize;++loop)
{
// See above
new (&data[loop]) T();
}
}
const vector<T>& operator= (vector<T> x)
{
// use copy and swap idiom.
// Note the pass by value to initiate the copy
swap(dataSize, x.dataSize);
swap(reserved, x.rserved);
swap(data, x.data);
return *this;
}
void reserve(unsigned int new_size)
{
if (new_size < reserved)
{ return;
}
T* newData = (T*)malloc(sizeof(T) * new_size);
if (!newData)
{ throw int(2);
}
for(unsigned int loop = 0; loop < dataSize; ++loop)
{
// Use placement new to copy the data
new (&newData[loop]) T(data[loop]);
}
swap(data, newData);
reserved = new_size;
for(unsigned int loop = 0; loop < dataSize; ++loop)
{
// Call the destructor on old data before freeing the container.
// Remember we just did a swap.
newData[loop].~T();
}
free(newData);
}
void push_back(const T &item)
{
if (dataSize == reserved)
{
reserve(reserved * 2);
}
// Place the item in the container
new (&data[dataSize++]) T(item);
}
unsigned int size() const {return dataSize;}
bool empty() const {return dataSize == 0;}
// Operator[] should NOT check the value of i
// Add a method called at() that does check i
const T& operator[] (unsigned i) const {return data[i];}
T& operator[] (unsigned i) {return data[i];}
void insert(unsigned int pos, const T& value)
{
if (pos >= dataSize) { throw int(1);}
if (dataSize == reserved)
{
reserve(reserved * 2);
}
// Move the last item (which needs to be constructed correctly)
if (dataSize != 0)
{
new (&data[dataSize]) T(data[dataSize-1]);
}
for(unsigned int loop = dataSize - 1; loop > pos; --loop)
{
data[loop] = data[loop-1];
}
++dataSize;
// All items have been moved up.
// Put value in its place
data[pos] = value;
}
void clear() { erase(0, dataSize);}
void erase(unsigned int erase_index) { erase(erase_index,erase_index+1);}
void erase(unsigned int start, unsigned int end) /* end NOT inclusive so => [start, end) */
{
if (end > dataSize)
{ end = dataSize;
}
if (start > end)
{ start = end;
}
unsigned int dst = start;
unsigned int src = end;
for(;(src < dataSize) && (dst < end);++dst, ++src)
{
// Move Elements down;
data[dst] = data[src];
}
unsigned int count = start - end;
for(;count != 0; --count)
{
// Remove old Elements
--dataSize;
// Remember we need to manually call the destructor
data[dataSize].~T();
}
}
unsigned int begin() const {return 0;}
}; //class vector
With your current memory handling, this vector would only work with plain old data types.
To handle all types, it must ensure that objects
are actually created (malloc doesn't do that),
destroyed (free doesn't do that),
and you can't reallocate memory with realloc, because complex objects are not guaranteed to remain valid if they are byte-wise copied to another location.
Looks like the answer can be found in your question: "When the object reference is returned, a method is invoked and the program segfaults. It seems it can't find this method and ends up in main_arena() in GDB. The type of the object is an inherited class."
You probably store base class instance T in the vector, but make push_back for the instance of the class inherited from T. In push_back {storage[_size] = T(item);} you cast (actually make copy constructor T:T(const T&)) item to T (this probably named 'type cut'), then get reference to T and invoke a method of the class inherited from T using virtual table of T where the method is not defined yet/abstract. Am I right?
To make it properly work you should put T* in the vector or shared_ptr/unique_ptr depending on the ownership terms you apply to vector elements.
Generally in vector you can store only POD (Plain Old Data) types.

c++ array class problems

Alright, so without going into detail on why I'm writing this class, here it is.
template<class aType>
class nArray
{
public:
aType& operator[](int i)
{
return Array[i];
}
nArray()
{
aType * Array = new aType[0];
_Size = 0;
_MaxSize = 0;
_Count = 0;
}
nArray(int Count)
{
aType * Array = new aType[Count*2]();
_Size = Count;
_MaxSize = Count * 2;
_Count = 0;
}
int Resize(int newSize)
{
aType *temp = new aType[newSize*2];
for(int i=0;i<_Count;i++)
{
temp[i] = Array[i];
}
delete[] Array;
aType * Array = new aType[newSize*2];
for(int i=0;i<_Count;i++)
{
Array[i] = temp[i];
}
delete [] temp;
_Size = newSize;
_MaxSize = newSize*2;
return 0;
}
int Push_Back(aType Item)
{
if(_Count+1 >= _Size)
{
Resize(_MaxSize);
}
Array[_Count] = Item;
_Count++;
return _Count - 1;
}
aType GetAt(int Index, int &ret)
{
if(Index > _Size-1)
ret = 1;
return aType();
ret = 0;
return Array[Index];
}
private:
int _Size;
int _Count;
int _MaxSize;
aType * Array;
};
It is supposed to be a std::Vector type object, without all the bells and whistles.
Problem is, it doesn't seem to work.
I basically start by going
nArray<string> ca = nArray<string>(5);
ca.Push_Back("asdf");
ca.Push_Back("asdf2");
int intret = 0;
cout << ca.GetAt(1,intret);
I get an Access Violation Reading Location error and it hits on the line
Array[_Count] = Item
in the Push_back function.
The problem seems to be that it's not treating the Array object as an array in memory.
I've spent time going through the code step by step, and I don't know what else to say, it's not operating right. I don't know how to word it right. I'm just hoping someone will read my code and point out a stupid mistake I've made, because I'm sure that's all it amounts to.
Update
So now I changed 3 initializations of Array in nArray(), nArray(int Count), and Resize(int newSize)
template<class aType>
class nArray
{
public:
aType& operator[](int i)
{
return Array[i];
}
nArray()
{
Array = new aType[0];
_Size = 0;
_MaxSize = 0;
_Count = 0;
}
nArray(int Count)
{
Array = new aType[Count*2]();
_Size = Count;
_MaxSize = Count * 2;
_Count = 0;
}
int Resize(int newSize)
{
aType *temp = new aType[newSize*2];
for(int i=0;i<_Count;i++)
{
temp[i] = Array[i];
}
delete[] Array;
Array = new aType[newSize*2];
for(int i=0;i<_Count;i++)
{
Array[i] = temp[i];
}
delete [] temp;
_Size = newSize;
_MaxSize = newSize*2;
return 0;
}
int Push_Back(aType Item)
{
if(_Count+1 >= _Size)
{
Resize(_MaxSize);
}
Array[_Count] = Item;
_Count++;
return _Count - 1;
}
aType GetAt(int Index, int &ret)
{
if(Index > _Size-1)
ret = 1;
return aType();
ret = 0;
return Array[Index];
}
private:
int _Size;
int _Count;
int _MaxSize;
aType * Array;
};
This is how my code was before. Anyway, the original problem was the fact that when I try to access a specific element in the array, it just accesses the first element, and it doesn't seem to add elements eather. It doesn't seem to be treating Array as an array.
int Resize(int newSize)
{
.
.
aType * Array = new aType[newSize*2];
At this point, instead of updating the member variable as you intended, you've actually created a local variable called Array whose value is discarded when you exit from Resize(). Change the line to
Array = new aType[newSize*2];
The same thing is happening in your constructors, they also need changing accordingly. Moreover, since the default constructor allocates an array, you should set the size members accordingly. You have too many of these: an array needs to keep track of current element count and maximum capacity, however you appear to have three members. What is the purpose of the third? Redundant information is bad, it makes code difficult to read and without a single point of truth it is easier to make mistakes.
With the code in Resize(), you can do better: the second copy is completely redundant.
int Resize(int newSize)
{
aType *temp = new aType[newSize*2];
for(int i=0;i<_Count;i++)
{
temp[i] = Array[i];
}
delete[] Array;
Array = temp;
_Size = newSize;
_MaxSize = newSize*2;
return 0;
}
Also, in
aType GetAt(int Index, int &ret)
{
if(Index > _Size-1)
ret = 1;
return aType();
ret = 0;
return Array[Index];
}
you need curly braces around body of the if(), just indentation on its own won't do the trick:
aType GetAt(int Index, int &ret)
{
if(Index > _Size-1)
{
ret = 1;
return aType();
}
ret = 0;
return Array[Index];
}
You have a number of problems. At a guess, the one causing problems so far is that your default ctor (nArray::nArray()) defines a local variable named Array that it initializes, which leaves nArray::Array uninitialized.
Though you probably haven't seen any symptoms from it (yet), you do have at least one more problem. Names starting with an underscore followed by a capital letter (such as your _Size, _MaxSize, and _Count) are reserved for the implementation -- i.e., you're not allowed to use them.
The logic in your Resize also looks needlessly inefficient (if not outright broken), though given the time maybe it's just my brain not working quite right at this hour of the morning.
Your array is not initialized by the constructors and resize function (working on local vars instead).
And is there a reason you want to store instances of string and not pointers to string (string *) ?
I think the answer after the changes is in moonshadow's reply:
aType GetAt(int Index, int &ret)
{
if(Index > _Size-1)
ret = 1;
return aType();
ret = 0;
return Array[Index];
}
This code will always return aType(), the last two lines will never be reached.
You might also want to check what happens if you start out with a default-constructed nArray. (Hint: you call Resize(_MaxSize); but what is the value of _MaxSize in this case?
Edit:
This outputs "asdf2" for me as it should be (with the initialization and the braces fixed):
template<class aType>
class nArray
{
public:
aType& operator[](int i)
{
return Array[i];
}
nArray()
{
Array = new aType[0];
_Size = 0;
_MaxSize = 0;
_Count = 0;
}
nArray(int Count)
{
Array = new aType[Count*2]();
_Size = Count;
_MaxSize = Count * 2;
_Count = 0;
}
int Resize(int newSize)
{
aType *temp = new aType[newSize*2];
for(int i=0;i<_Count;i++)
{
temp[i] = Array[i];
}
delete[] Array;
Array = new aType[newSize*2];
for(int i=0;i<_Count;i++)
{
Array[i] = temp[i];
}
delete [] temp;
_Size = newSize;
_MaxSize = newSize*2;
return 0;
}
int Push_Back(aType Item)
{
if(_Count+1 >= _Size)
{
Resize(_MaxSize);
}
Array[_Count] = Item;
_Count++;
return _Count - 1;
}
aType GetAt(int Index, int &ret)
{
if(Index > _Size-1) {
ret = 1;
return aType();
}
ret = 0;
return Array[Index];
}
private:
int _Size;
int _Count;
int _MaxSize;
aType * Array;
};
#include <string>
#include <iostream>
using namespace std;
int main()
{
nArray<string> ca = nArray<string>(5);
ca.Push_Back("asdf");
ca.Push_Back("asdf2");
int intret = 0;
cout << ca.GetAt(1,intret);
}