Pointers

1. Pointers • A pointer is an address • All data is stored in memory in some location that is indexed with an address • Can refer to variables by name or by memory address • Variable name is an alias for the address in memory • Purpose of pointers • Provide shared access to common data in memory • Resource efficiency • Build dynamic data structures • A dynamic array that can grow • Control allocation and de-allocation of memory

2. Pointers • Pointers are distinguished by the type of pointee • Type double* is not the same as int* • Pointers are uninitialized until assigned • Dereferencing an uninitialized pointer is not a good idea • Dynamic allocation via new • Operator new allocates memory from heap, returns address • Manual de-allocation via delete • Forgetting to delete means memory is orphaned • Accessing deleted memory has unpredictable results

3. int num; int *p, *q; p = new int; *p = 10; q = new int; *q = *p; q = p; delete p; delete q; //bad idea, q already deleted! q = NULL; //NULL is zero pointer Pointer Operations

4. Use of Pointers struct studentT { string first, last; string address, phone; }; struct courseT { string dept, name; Vector<studentT *> students; }; • A course has pointers to enrolled students • Allocate studentT record in heap for new student • Each course a student enrolls in will store pointer to that student's record. • Saves space by not repeating student information • If student gets new phone number, it changes in one place only!

5. Pointers and Dynamic Arrays int *arr = new int[10]; for (int i =0; i < 10; i++) arr[i] = i; delete[ ] arr; Declare a pointer to an array of ten integers Initialize all ten positions Deallocate the array Always use delete[ ] if the array was declared with new

6. References • see.stanford.edu/materials/icspacs106b/Lecture12.pdf