Pointer arithmetic

[dan]

Hello,
An Iterator class declares a data member that points to the current
index of an array within a container class. It also implements a
member function that determines whether or not the data member is
pointing to the last index in the array using pointer arithmetic.

class CIterator
{
public:
CIterator(CContainer& c) : myContainer,
mypData(myContainer.mypArray) {}

void Reset() { mypData = myContainer.mypArray; }
bool IsEnd()
{
return ((mypData - myContainer.mypArray) >=
myContainer.mySize);
}

private:
CContainer& myContainer;
int *mypData;
};

My question is in regards to the way c++ points to memory. If {
mypData = myContainer.mypArray; } assigns the address of the first
element in the array to mypData, then how is it that ((mypData -
myContainer.mypArray) >= myContainer.mySize); the first operand which
is basically an address in memory, (correct?) can relate to the second
operand (mySize) which is an int with a relational operator? the 2
data types don't seem compatible.

Daniel

 

[Jeff Schwab]

Hello,
An Iterator class declares a data member that points to the current
index of an array within a container class. It also implements a
member function that determines whether or not the data member is
pointing to the last index in the array using pointer arithmetic.

class CIterator
{
public:
CIterator(CContainer& c) : myContainer,
mypData(myContainer.mypArray) {}

void Reset() { mypData = myContainer.mypArray; }
bool IsEnd()
{
return ((mypData - myContainer.mypArray) >=
myContainer.mySize);
}

private:
CContainer& myContainer;
int *mypData;
};

My question is in regards to the way c++ points to memory. If {
mypData = myContainer.mypArray; } assigns the address of the first
element in the array to mypData, then how is it that ((mypData -
myContainer.mypArray) >= myContainer.mySize); the first operand which
is basically an address in memory, (correct?)

No, it's difference between two addresses. It's usually a signed