C++ Dynamic Memory Allocation

An array is a fixed size that must be known when it is declared.
In some cases, you may not know how big to make the array at compile time.
One way around this is to use pointers and explicitly manage memory yourself.
In C++, new is used to allocate memory.

The basic syntax is:


Point    *ptr1;
Point    *ptr2;
Point    *ptr3;
Point    **ptr4;
Point    *ptr5[];

ptr1 = new Point;           // calls the default constructor
ptr2 = new Point(7,200);    // calls the constructor that takes 2 int arguments
ptr3 = new Point[N];        // For arrays

The new will allocate the correct amount of memory and return a pointer to this memory, which is stored in ptr.

To deallocate the memory, use the keyword delete:


delete ptr1;
delete ptr2;
delete [] ptr3; // For arrays

Use NULL to indicate a pointer that doesn't point to anything: int *ptr1 = NULL; You may need to include the stdlib system header.
Note: if you do not free the memory correctly, you have can have what is called a dangling pointer (an address that points to memory that has been freed or re-used), or one of the most common, and insidiuous, errors in C/C++: a memory leak (memory that is no longer pointed to, but that has not been freed).
Eventually your program will run out of memory and crash.