3.1 malloc and new

Let us consider this example:

class X
{
    int i;
    int j;
  public:
    X(void);
    ~X(void);
};

X::X(void)
{
  i = j = 0;
}

X::~X(void)
{
  cout << "X destructor is called" << endl;
}

This class definition is hardly exciting. However, it serves its purpose to illustrate the differences between malloc and new.

First, let us consider the following code using malloc to create an object of class X:

X *myX;
myX = (X*)malloc(sizeof(X));

Next, let us consider the ``equivalent'' code to create an object of class X, but this time using new:

X *myY;
myY = new X;

Now, what is different about that myX points to, and what myY points to?

The difference is that the data members of what myX points to is not initialized. However, the data members, i and j of what myY points to are initialized to 0.

In other words, malloc simply allocates enough memory from the heap, and returns a pointer. However, new allocates memory like malloc, but it also invokes the default constructor X::X(void).

This is one important difference between malloc and new.