I need to understand how to manipulate data in various index positions in a dynamically allocated character array in c++. I am making a quack (queue/stack). The variable I am concerned with is 'items.'
Here is the class definition for Quack:
class Quack
{
public:
static const char YOUR_NAME[]; // used for printing out programmer's name
static const bool PREMIUM_VERSION; // used to designate Regular vs. Premium
Quack(int capacity, int growBy = 0);
// capacity: # of slots in array
// growBy: # of slots to add to array when it grows, 0 means "don't grow"
~Quack(void);
bool pushFront(const char ch); // push an item onto the front
bool pushBack(const char ch); // push an item onto the back
bool popFront(char& ch); // pop an item off the front
bool popBack(char& ch); // pop an item off the back
void rotate(int r); // "rotate" the stored items (see note below)
void reverse(void); // reverse the order of the stored items
int itemCount(void); // return the current number of stored items
void printArray(std::ostream& out) // print contents of array
{
unsigned int ch;
out << "[ ";
for (int i = 0; i < capacity; i++) {
ch = static_cast<unsigned char>(items[i]); // avoid sign extension
if (ch == '-') // print in hex, because using '-' for 0xCD
goto printHex;
else if (ch >= '!' && ch <= '}') // ASCII text character
out << static_cast<char>(ch) << ' ';
else if (ch == 0xCD) // print 0xCD as '-'
out << "- ";
else // print everything else as hex
goto printHex;
continue;
printHex:
out << std::setw(2) << std::setfill('0') << std::hex << ch << ' ';
}
out << ']' << std::endl;
}
private:
char *items;
int nItems;
int capacity;
int growBy;
int *front;
int *back;
public:
friend std::ostream& operator<<(std::ostream& out, Quack *q);
};
Now, here's the Quack constructor:
Quack::Quack(int capacity, int growBy) :
capacity(capacity),
growBy(growBy),
nItems(0),
items(new char[capacity]),
front(NULL),
back(NULL)
{
}
I understand that each instance of Quack has a char variable 'items' which is a pointer to a new character array. What I don't understand is how to reference the items in the array. For example, if I want to refer to index position 0 of the new character array, do I say items(0) , or items[0] , or is it something completely different?
Thank you
As you understood correctly, items
is a char array and each instance of Quack
has its own variable items
. Accessing a dynamically allocated array and a statically allocated array is the same. They are allocated in contiguous memory locations.
char arr[24]; // Allocate 24 bytes in contiguous memory locations in stack
char* arr = new char[24]; //Allocate 24 bytes in contiguous memory locations
// in heap
You can access the variable in any of the following ways:
1. Quack q;
cout << q.items << endl; //Print the char array
cout << q.items[1] << endl; // Print the second index position of items
2. Quack* qptr = new Quack();
cout << q->items << endl; //Print the char array
cout << q->items[1] << endl; // Print the second index position of items